A contrafact is a new melody written over a well-known tune's chord changes — same harmony and form, different tune entirely. Composers used it to write fast over changes a band already knew, and — especially in the bebop era — to sidestep royalties on someone else's published melody, since a chord progression itself can't be copyrighted the way a melody can. "I Got Rhythm" is by far the most contrafacted set of changes in the book (see Rhythm Changes); a few tunes instead rebuild an existing standard's changes with Coltrane's own cycle. Search by tune, composer, or the standard it's built on.