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3702215
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Patent number 3,702,215
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Issue date Nov 7, 1972
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G02 - OPTICS
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3660818
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Patent number 3,660,818
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Issue date May 2, 1972
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G02 - OPTICS
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3637931
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Patent number 3,637,931
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Issue date Jan 25, 1972
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G02 - OPTICS
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3559185
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Patent number 3,559,185
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Issue date Jan 26, 1971
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G09 - EDUCATION CRYPTOGRAPHY DISPLAY ADVERTISING SEALS
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3520589
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Patent number 3,520,589
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Issue date Jul 14, 1970
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G02 - OPTICS