sample words: 500 nonzero of 500
first letter moved outside {ah,bh,ch}                500 / 500 zero
last letter set to ah/bh/ch (final-entry condition)  500 / 500 zero
extended-Steinmann pair inserted                     500 / 500 zero
one non-y letter replaced by a y letter (odd parity) 500 / 500 zero
cyclic image                                         500 / 500 equal
flip image                                           500 / 500 equal
parity image (identity on even-y words)              500 / 500 equal
PASS