Abaya, E. F. (1996). Coding telephone number to avoid “wrong numbers”. Philippine Engineering Journal.
Lua i Stíl Chicago (17ú heag.)Abaya, Efren F. "Coding Telephone Number to Avoid “wrong Numbers”." Philippine Engineering Journal 1996.
Lua MLA (9ú heag.)Abaya, Efren F. "Coding Telephone Number to Avoid “wrong Numbers”." Philippine Engineering Journal, 1996.
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