CROSBY PHILIP B. (1980). QUALITY IS FREE THE ART OF MAKING QUALITY CERTAIN. MENTOR BOOKS.
Lua i Stíl Chicago (17ú heag.)CROSBY PHILIP B. QUALITY IS FREE THE ART OF MAKING QUALITY CERTAIN. NEW YORK: MENTOR BOOKS, 1980.
Lua MLA (9ú heag.)CROSBY PHILIP B. QUALITY IS FREE THE ART OF MAKING QUALITY CERTAIN. MENTOR BOOKS, 1980.
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