US2482039A - Secret communication employing signal sequence switching - Google Patents

Description

P 1949- L. A. THOMPSON 2,482,039

SECRET COMMUNICATION EMPLOYING SIGNAL SEQUENCE SWITCHING Flled Sept. s, 1945 2 Sheets-Sheet 1 I I I I 6? 56 I I I l I l I l I I I I .I I l I I I I I l I I l I I I I I I I I I I l I I I I I I I I I I I I I I 85 I I I l ---I I I l I l I I l. J L AD/O I 1 l 3,2 i I: AHE' B-PF fix; I I I I INVENTOR.

/ v (00/5 A. THOMPSON A TTOENEYS p 1949- L. A. THOMPSON 2,48 ,039

SECRET COMMUNICATION EMPLOYING SIGNAL SEQUENCE SWITCHING Filed Sept. 6, 1945 2 Sheets-Sheet 2 B fig A r TOEA/EYS Patented Sept. 13, 1949 UNITED STAT SECRET COMMUNICATION EMPLOYING SIGNAL SEQUENCE SWITCHING Louis A. Thompson, Rocky River, Ohio, assignor to NEA Service, Inc., Cleveland, Ohio, 2. corporation of Delaware Application September 6, 1945, Serial No. 614,772

6 Claims. 1

My invention relates to switching apparatus, particularly sequence switching for signal transmission.

It is an object of my invention to provide improved methods and apparatus for signal transposition and the security transmission of information.

A further object of my invention is to avoid transients or effects recognizable as transitions or transfer points in the electrical transmission of intelligence.

A further object is to provide electrical continuity between unrelated signal segments. Still another object of my invention is to transfer electrical signals back and forth between circuits with high precision so as to avoid any overlap between signals and to avoid also any period during which no energy is present in the system.

Still another object of my invention is to control signal switching photo-electrically.

Further object of my invention is to control selection of channels for signal transmission by selectively blocking various channels.

Other and further'objects, features and advantages of my invention will become apparent as the description proceeds.

In carrying out my invention in accordance with a preferred form thereof, I provide a punched tape in conjunction with a source of light and a photo-electric tube for producing channel energization and blocking voltages in accordance with the pattern of slots punched in the tape, which is caused to travel at a uniform rate of speed preferably synchronized with other apparatus. A plurality of circuits is provided each controlled by a photo-electric tube associated with one of therows of the slots in the moving tape. There may be a plurality of connections through which input signals are received where several signals are to be transposed among the various channels for security purposes. For the sake of simplicity however, the invention will be explained in connection with an arrangement in which different signal elements or segments of a single signal differing in time relation are transposed by means of the apparatus for the purpose of making the signal unintelligible to an unauthorized receiver. Preferably -in this case memory apparatus synchronized with the moving tape is employed for the purpose of providing different segments of the same signal differing in time of occurrence.

Means are provided for causing signal output to be transmitted from one of the circuits at a time and preferably means are provided for converting the input signals into frequency variations to simplify the elemination of transition or transfer effects. The frequency modulatedoutput signal is amplified and severely limited so that no possible difference in signal level occurs at the transfer points where the circuit is switched from one channel to another. After limitation of the signal, it is filtered to reconvert the transposed signal wave to one having only sine wave components within the frequencymodulation frequency range.

The output signal is transmitted by any suitable medium such as land wire, carrier, radio or the like. For reception of the signal suitable apparatus is provided for reversing the operations performed on the signal prior to the transmission so as to rearrange the signal segments in the original order before application to an ordinary receiving device such as a telephoto exposure head, telephone, telegraph or teletype receiver or the like.

A better understanding of the invention will be afforded by the following detailed description considered in conjunction with the accompanying drawing in which Fig. 1 is a circuit diagram schematically illustrating an embodiment of my invention as used in the transmission of transposed signals. Fig. 2 is a schematic diagram of receiving apparatus adapted for use with the apparatus of Fig. 1, and Fig. 3 is a diagram of a combined switching, signal coding, and memory apparatus utilizing a punched tape for control.

Referring to the drawings it is assumed that signals for transmission are applied to an input terminal ll. Suitable means such as a memory apparatus [2 are provided for recording and making available elements or segments from the input signal differing in time relation. A plurality of channels, in this case represented as three in number, are provided for passing different signal elements. These three channels are represented by amplifiers 13, M, and i5 included in the respective channels. A signal sequence switching device It represented by the portion of the apparatus within the dotted lines is provided for control of the sequence of signal elements supplied to the output circuit, which includes an amplifier ll to which the out puts of the amplifier l3, l4 and [5 are connected in parallel.

Memory apparatus is arranged to provide three signal output circuits I8, 19 and 2|. Preferably means are provided for converting the signals to frequency modulated signals. For example three oscillators 22, 23 and 24 may be provided, each having reactance-tube modulating means 25, 26

and 21, respectively, interposed between the circuits l8, I9 and 2| and the oscillators 22, 23 and 24, respectively. For the sake of simplicity the oscillators 22, 23 and 24 have been shown as separate units; but preferably I employ a single fixed-frequency oscillator beating with three variable frequency oscillators, each controlled by one of the signal circuits l8, l9, and 2| and having a different average frequency. For example a frequency of 100 kilocycles may be chosen for the fixed-frequency oscillator, and; the. mid-range frequencies of the variable oscillators may be 101, 102, and 103 kilocycles respectively. It will be understood, of course, that these specific numerical values are given merely by way of illustration and that the invention is not limited to any specific values.

The signal switching device I6 includes a movable beam interceptor or a shutter means, a radiant beam source and a plurality of radiant energy responsivedevices. The beam interceptor is illustratedas a moving tape 2 8, driven at a uniform rate ofspeed by a drum 2-9. The radiant beam source most conveniently takes the form of a lamp 3|. The radiant-energy responsive devices preferablytake the form of photoelectric tubes 32,33, and: 34. Means are provided for controlling-the transmission of signals through the amplifiers 13-, I4 and I in response to the photoelectric- tubes 32, 33 and 34. The tape 28 is provided with a plurality of rows of slots in this case three rows of slots 35, 36 and 3'! corresponding in number to the number of photoelectric tubes and the number of transmission channels. Prefrably a beam-focusing arrangement, represented schematically by a single lens 38 and a slot 39 are provided in order to produce a thin ribbon oilight spread across the tape 28, or a plurality of beams aligned transversely across the tape 28, striking the respective slots 35, 5:18 and 37. For the sake of simplicity of explanation it is assumed thatjlig htfrom the lamp 3| has been broken into three separate beams 4!, 42, and- 49 adapted to be reflected by mirrors 44, 45 and 46, against the photoelectric tubes 32, 33 and 34, respectively. The complete paths of; all the light beams have been shown, although with the tape 28 in the position illustrated, only the light beam 4-2-is free 3 to pass through the associated'slot 41in the tape -28 and to strike the associated photo-electric oscillator 22 and a blocking tub 52. The amplifier I3 also has connections 53 tapping voltage therefrom and supplying a pair of unilateral deviees such as full wave rectifiers 54 and 55. Similar devices are associated with the amplifiers l4 and I5. The output connections 56, 5! and 58 qf the amplifiers are connected in parallel directly or indirectly to a common output line 59 supplying the input to the amplifier IT,

The direct current-amplifier tube 48 has an anode or plate ,6 connectedto a suitable source V ltager. epresen ted by the symbol Bjand has a cathode 8-2 inseries with the primary winding 6312 an np t fq m 1 t am l e L3, Alsoeonneeted in series with the winding 6. istbe s gnal ick-un ube 4 av nsa cathod "65 connected to the cathode 86 of blocking tube 4 52. A cathode resistor 61 is connected between the cathode 65 of the blocking tube 52 and ground. The plate or anode 68 of the blocking tube 52, associated with the amplifier I3, is connected through a conductor 69 to output conductors H and '52 associated with the rectifiers tapped into the other amplifiers. Thus the line H is connected to a rectifier 13 having leads from the amplifier l4, and the line 12 is connected to the output terminal of the rectifier 14 energized from the amplifier {-5, The blocking tube 15 associated with the amplifier I4 is supplied with the direct current either from the rectifier 55 associated with the amplifier +3 on the rectifier l9 associated with the amplifier [5. In like manner each amplifier is provided with a plurality of unilateral devices or rectifiers, each one supplying direct current to the blocking tube of one of the other amplifiers.

In order to eliminate the transient efiect of variations in amplitude of transposed'wave segments and to suppress any indications of the points of transposition, a push pull limiterl'tis provided in -the output side of the amplifier I! designed for severely limiting the wave. For converting the output of the limiter TI from-a rectangular wave or one having square tops, to

a wave containing only sine wave components of the frequencies represented: by the output ofthe oscillators 22, 23- and 24-a-band-pass filter 18: is provided. Where the numerical values'of the frequencies employed are as previously assumed, so that the output-frequencies of oscillators 22, 23 and 24 average- 1000,2900, and 3000 cycles, respectively, the filter 18 has band-passing frequencies lying in the regionbetween zero and 5000 cycles, for example. Preferablyan amplifier 18 is provided for amplifying the output of the band-pass filter 18 and supplying it to a suitable transmission channel, which may take the form of a wire or-carrier circuits, but for the sake of illustration is represented as a radio transmitter 8| including-radiator elements'82.

Preferably the tape 28 is so arranged as-to be coordinated with the-memory apparatus L2 so-that the slot punching of the tape 28 maybe employed also-for controlling the transposition arrangement and coding of the memory-device 12. Any suitable form of a memory apparatus may be employed. The; arrangement illustrated comprises a travelling, magnetic wire, tape or disc 84 having means for synchronizing itself with the punched tape 28. This is indicated schematically in the drawings-bymechanical connections consisting of the shaft 85, bevel gears 88 and8'l; and a shaft'88 connected to thesprocket drum 29 drivingthe tape "28'. The mernorydevice I2 is provided with a signal-recording electr c-magnet 89, a plurality of signal pick-up.-electro-magnets "9|, 92-and 93 or -more (not shown) and an erasmagnetic record 84 by the recordingmflgnet 89,

before it is wiped oiT-or erased'by magnet 94. The erasingmagnet' 94- may be a permanentmagnet or a high-frequency electromagnet. The angular spaeine between the pick-up heads or electroma ne s 1 921.a may, e o late to th linsarg pac ns tween. h t ail ng e ds. of th successive slots 95, 96' and 91" of the tape ZB' th at anode B8 of the blocking tube 52.

either thesame length of time is required for the magnetic disc 84 to move through a unit spacing as for the tape 28, or the time ratio is an integral number. For the sake of simplicity of explanation, a simplified pattern or arrangement of slots is shown but it is to be understood that in practice a more complicated code may be and preferably is employed. The slots punched in the tape 28 may be of the same lengths or different lengths and the spacing of successive slots may be difierent in accordance with the code employed. It is unnecessary however to employ great accuracy in the length of the slots, the determining factor is the space from the trailing end of one slot to the trailing end of the next, for example, from the end 98 of the slot 96 to the'end 99 to the slot 95. Preferably, as indicated, trailing ends of the slots overlap for reason which will be explained. The amount of overlapping and any variations therein have no effects on the accuracy and precision of the operation of the signal transposition and sequence switching.

' Since the recording heads 9|, 92 and 93 of the memory apparatus I2 are operated at different angular positions, a signal occurring during a given time interval will be reproduced at successively later times by the heads SI, 92 and 93. The arrangement of the tape 28 is such that the portions of a signal occurring during successive time intervals are delivered to a channel separately as signal segments, and the signal segments are rearranged and retransmitted out of their natural order. Thus when the light beam passes through only one of the slots in the central row such as slots 96 and 41, the photo-tube 33 is illuminated causing the amplifier I4 to operate. Similarly for the other amplifiers and the channels in which they are located. However, when light beams pass through two overlapping slots, one channel blocks the other so that only one channel is efiective.

When the tape 28 is in such a position that the light passes through both the slot 95 and the slot 96, the poto tubes 32 and 33 are illuminated. Current passes through tubes 32 and 33. Passage of current through the photo tube 32, positively biases the D.-C. amplifier 48 to render it conducting. Voltage is applied from the terminal B through the tube 48 and the input transformer 63 to the anode 68 of the signal relay device or pickup tube 59 thereby energizing it. The latter is thereby pre-set so as to permit a signal from beat frequency oscillator 22 to afi'ect the Pick-up tube 49 as soon as it becomes conducting. The signal pick-up tube I02 had previously been rendered conducting through the action of light falling on the photo tube 33, so as to energize the amplifier I4 and supplypositive voltage to the Consequently the cathode B5 of the pick-up tube 49 is positively biased by the flow of current through the cathode resistor 61 of the tube 52. As soon as the tape 28 moved to the point at which the edge 98 of the slot 96 cuts-off the light beam 42, the tubes IIlI and I82, amplifier I4, the rectifier I3 and the blocking tube 52 lose energization. At the same instant the potential of the cathode 95 falls to zero and the tube 49 becomes responsive to pass segments to the amplifier I3. Under these circumstances the amplifier I3 is first pre-set so that the signal pick-up tube 49 and the amplifier I3 'may pass current as soon as current is cut-off from blocking tube52; In a similar manner the interception of lights at the trailing edge of each slot very precisely fixes the instant of signal transfer to the ne'x't'cliannel. In the pattern arrange ment of slots shown, in the drawing, for the sake of illustration, light beams will pass successively through the slots 91, 9B and assuming that the tape 28 is traveling downward. Consequently signal segments from the memory apparatus pickup heads SI, 92 and 93 will be sent successively through the channels I3, I4 and I5 and applied in this order to the common output line 59. However since the magnetic recording tape or disc 84 is traveling in a direction from the pick-up head 9! to 93 the signal segments actually occurring last are transmitted first so that confusion is introduced in the transmitted signal. The speed of the operation is such that very short segments are transposed and'consequently the signal emitted from the radio transmitter 8| is not transcribable or decipherable. By suitable arrangements of the slots in the tape 28 other and more complicated transpositions are provided making it still more diflicult to decipher the transmitted signal.

In order to receive and decode the signal it is necessary to have corresponding apparatus employing a transposition controlling and decoding tape corresponding exactly with the tape 28. A suitable receiving apparatus may comprise a radio receiver III having antennae II2 corresponding to the transmitter antennae 32, a preamplifier IIU, a push pull limiter II3 for removing the fading eiiect, preferably an additional amplifier I It, memory apparatus I I5 corresponding to the transmitter memory apparatus I I2, and signal switching apparatus H9, corresponding to the. transmitter signal switching apparatus .I9. By limiting the output to a predetermined value independent of input strength or fading, the limiter I I3 overcomes the effect of fading. The principle of operation of limiters is described in Basic Radio, by Hoag, 1942 edition, page 2'74, referring to Fig. 33C and in Ultra-High Frequency Techniques, by Brainerd et al., 1942 edition, pages 179, 267 and 283. The switching apparatus H6 is provided with three output lines H1, H8 and I I9 corresponding respectively to the output lines 58, 5'! and 58. Preferably the receiver includes limiters I2I, I22 and I23 in lines H1, H8 and H9, and also amplifiers I24. The output terminals of the amplifiers I24 are connected directly or indirectly in parallel to a pair of conductors I25 to which a suitable device I28 is connected such as a telephoto exposure head, a teletypewriter, a

telephone receiver including a detector or other reception device, depending upon the input signal to the transmitter. The memory apparatus H5 and the signal sequence switching apparatus IIIi are provided with driving motor means I21 for operating the two devices H5 and IIG. Suitable means (not illustrated) are provided for causing the motor 83 at the transmitter and the motor IZI at the receiver to operate synchronously and exactly in phase. Such means may take the forms of synchronizing drives or synchronizing signals such as employed in telephoto and television circuits.

The signal switching apparatus I I9 is indicated in block form but is preferably identical with the arrangements shown within the dotted line III of Fig. 1. It includes tape such as the tape 28 of Fig. 1 which is identical there with same punching arrangement. In case the receiving apparatus indicated in Fig. 2 should be located in such a position that it may fall in enemy hands during military use or there is danger that unauthorized operators of the signal transmission circuits may obtain access thereto during cominercial use, the tape: of the receiving apparatus removed before leaving the receiving apparatus ungu'arded. Without the. proper tape.- serving as.:-.a key tov the transposition it is; not possible. for an'unauthorized personeverr-with similar receiving. apparatus to obtain signalswhich convey intelligence. Even if received signals should be recordedand should; be: examined by decoding experts allowed a considerable. period of time, decoding Wouldbe impossible because the points of transition are not detectable. Thesignal segments into which the original segment was cut fit together. without revealing transition points since only frequency changes are involved and opera-tesrvery precisely in starting the transmission of. signal segment over one channel at the instantof termination of the transmission over another. channel. There are no transition; or decay efiectsbywhich a person attempting to decode the recorded signal can observe the points of transition.

'I heonly way of decoding the signal segment in theoriginal order is to employ a tape in the switching, apparatus i it at the receiver which is identical with the tape 28' at the transmitter. Consequently the simple operation of removing such a tape renders it impossible for unauthorized persons to receive signals even though they may obtain access to-the receiver. Thus the apparatus maysafely be employed for security purposes even if those operating the receiver should find itFi-mpossibleto retain control thereof and should noteven have. time to destroy the receiver. The tapemay; be composed of inflammable material or of metal, but even if composed of metal it is readily destroyed: since thin metal would be employed. Even though the light metal tape may not be consumedby fire it will be destroyed by the heat. For example it'may also be destroyed by passage of electrical current to heat it to glowing temperatures. This will serve to damage it to such an extent that it will not operate and that the slot coding is not reproducible.

Thin metal tape has the advantage of maintenance of accuracy of slot spacing independently of humidity conditions.

In order to simplify the precise synchronization of the moving elements of the memory apparatus i2 andthe moving tape 28 f the signal sequence device it, a tuning fork drive or a moving light'interceptor may be employed as the common moving element for both devices. For example a slotted'motion picture film having sound tracks at'the edge may be employed for the operation of both the photo- electric cells 22, 23 and 24 and forenergizing the memory device units photoelectrically. Preferably a steel tape is employed for the sake of accuracy. As indicated in Figure 3, a tape {29 is employed composed of steel having slots I28, I29 and lfii cut therein with slot spacing corresponding to the spacing of the magnetic pick-up-head's SI, 92 and 93 arranged along the edge I32 of the tape lZ'i. It should be understood that the recording head 89 is arranged in advance of. the pick-up heads 9!, 92 and. 93 and that an erasing magnet 94 may be provided as previously described.

While I have described my invention as embodied in concrete form and. as operating in a s-peeificmanner in accordance with the provisions of the patent statutes it should be understood that I donot limit my invention thereto, since various modifications thereof will suggest themselves to those skilled in the. art without departing from 8 the'spirit of my invention,- the scope of which 'is set forth in the annexed claims.

I claim: 7

1. Signal sequence switching apparatus. comprising in combination a. plurality of transmis mison channels, a plurality of blockingdevices, each one adapted to block one of said. channels when. energized, means providing a plurality of lightbeams, a moving, tape arranged to intercept said light beams with each beam striking a different distance from the edge of the tape, said tape having. longitudinal rows of slots, each row of slots passing through one of said light beams, whereby said light beams are intermittently passed and-intercepted as the tape moves, said slots being arranged according to a fixed pattern and each slot longitudinally overlapping a slot in. another row, a plurality of photo-electric responsive devices beyondsaid tape with respect to said light providing means, direct current amplifiers actuated by said photo-electric devices, and connections from each one of said amplifiers tooneof said channels. for energizing the same, unilateral means between each of said amplifiers and allof the blocking devices except the one associated with the channel energized by the same amplifier, uniiateral means being connected to said respective blocking devices for energizing the same in response to amplifier output, memory apparatus for recording the input to each blocked channel and for subsequently transferring the recorded signals to said. channels.

2. A signal sequence switching apparatus. comprising in combination a plurality of transmission channels, a plurality of blocking devices, each one adapted to block one of said channels when energized, means providing a plurality of light. beams, moving tape arranged to intercept said light beams with each beam striking a differentdistance from the edge of the tape, said tape having longitudinal rows of slots, each row of slots passing through one of said lightbeams whereby said light beams are intermittently passed and intercepted as the. tape moves, said slots being arranged according to a fixed pattern and each slot longitudinally overlapping a slot in another row, a plurality of. photo-electric responsive devices beyond. said tape with respect to said light providing means, direct current amplifiers-connected to said photo-electric devices, connections from each of said amplifiers to one of said channels for energizing the same, and simultaneously energizing each of said blocking devices except the one associated with the channel energized by said amplifier.

3. A signal sequence. ap aratus comprisingin combination a plurality of transmission'channels, a plurality of blocking devices each one adapted to. block one of said channels when energized, means'provi'ding a plurality of light beams, moving. shutter meansarranged to intercept said light beams with each beam striking a difierent distance from the edge or" the shutter means, said shutter means having rows of slots, each row passing through said light beam whereby said light beams are intermittently passed and inter.- cepted as the shutter means moves, said slots being arranged according to a predetermined pattern and each slot longitudinally overlapping a slot in another row, a plurality oi photo-electric responsive devices beyond said shutter means with respect. to said light providing means, direct current amplifiers actuated by said photo-electric devices, and connections between said; channels and said direct current amplifiersforprecondi- 9 tioning each channel to be energized with corresponding light beams permitted to pass through said shutter means and for energizing the blocking means of the other channels simultaneously therewith, whereby each channel becomes finally energized when the channel is unblocked.

4. Signal sequence apparatus comprising in combination a signal source, a plurality of transmission channels, a plurality of blocking devices each one adapted to block said channel when energized, means providing radiant energy beams, moving shutter means arranged to intercept and pass such beams intermittently according to a predetermined pattern, each of said radiant energy beams corresponding to one of said channels, a signal relay device for each channel controlling transmission of received signals through it, each of said signal relay devices being of the type effective to permit transmission through its channel only when energized, means responsive to passage of the radiant energy beam corresponding to a given channel for simultaneously energizing the signal relay device of the corresponding channel and energizing the blocking means for the other channels, whereby the interception of the radiant energy beam terminates the blocking of a given channel, releases such channel for signal transmission, and signals are transferred in sequence from one channel to another according to the pattern of said shutter means.

5. Signal sequence apparatus comprising in combination a plurality of transmission channels, a plurality of blocking devices each associated with one of said channels, a source of radiant energy, a plurality of radiant energy responsive devices, a moving radiant energy interceptor with slots in rows each corresponding to one of said energy responsive devices, and connections from each of said energy responsive devices for energizing one of said channels and blocking the remainder, whereby signals are .-passed through said channels in accordance with a code determined by its slot arrangement of the said moving interceptor.

6. The method of signal transmission which comprises recording of the signal to be transmitted in segments occurring in difierent intervals of time, transmitting signal segments through separate channels, transposing the sequence of transmission through said channels in accordance with a predetermined code with transmission through only one channel at a time, combining the transposed signal segments to form a continuous unbroken transmission, limiting the output amplitude to suppress decay effects at the instants of transfer, transmitting the output of the limiter, receiving such output and recording successive signal segments, transposing the signal segments in accordance with the same transposition code employed in the transmitter for restoring the original signal sequence in difierent channels, limiting the output in each channel and combining all the outputs for utilization in a receiving device.

LOUIS A. THOMPSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,048,081 Riggs July 21, 1936 2,094,132 Miller Sept, 28, 1937 2,282,046 Goldsmith May 5, 1942 2,300,664 Francis Nov. 3, 1942 2,364,210 Guanella Dec. 5, 1944 2,380,982 Mitchell Aug. '7, 1945 2,401,888 Smith June 11, 1946 2,403,561 Smith July 9, 1946 2,406,353 Myers Aug. 27, 1946 Certificate of Correction Patent No. 2,482,039 September 13, 1949 LOUIS A. THOMPSON d that errors appear in the pr ted specification of the above tube 59 It is hereby eertifie numbered patent requiring correction as follows:

Column 5, line 48, for terminal B read terminal 13+; line 51, for read tube 49; and that the said Letters Patent should be read with these correcti m to the record of the case in $111.36 Patent Oflice.

the same may confer Signed and sealed this 17th day of January, A.

one therein that THOMAS F. MURPHY,

Assistant Commissioner of Patents.

flertificate of Qorrection September 13, 1949 Patent No. 2,482,039

LOUIS A. THOMPSON It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 5, line 48, for terminal B read terminal 13+; line 51, for tube 59 read tube 4.9; and that the said Letters Patent should be read with these corrections therein that the samemay conform to the record of the case in the Patent Ofiice.

Signed and sealed this 17th day of January, A. D. 1950.

THOMAS F. MURPHY,

Assistant Commissioner of Patents.

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