The purpose of this book is to demonstrate that (in the author's own words):GT the Gospel of Thomas is neither independent of nor directly dependent on the Greek synoptic Gospels.If Thomas was influenced by Matthew, Mark, Luke (and John), it is only insofar as the latter are mediated through the first Syriac Gospel record: Tatian's Diatessaron (p.15)
D.C. Parker (Wed,) studied this question.