Variant versions of changes are common due to the popularity of adding interest with chord substitutions, passing chords and changes of chord quality. Bebop players, for instance, would often superimpose series of ii–V (passing sequences of minor seventh and dominant seventh chords) or other substitutions for interest or in order to discourage less experienced musicians from "sitting in" on the bandstand. The opening I chord was often B6 in Gershwin's original, but beboppers changed it to BM7 or B7. For instance, the B section may appear as follows: