Simple past tense and past participle of cowrite.(verb)
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Use "cowritten" in a sentence
"This is the book that Larry Page read at Stanford, cowritten by the professor he hired to head research at Google."
"He has cowritten several Peter Pan novels with Dave Barry and is writing a series of YA thrillers set in Disney theme parks."
"McBride came out of nowhere a few years ago with the film The Foot Fist Way also cowritten with Best, which has served as the template for the rest of his career to date."