Assumption (A): a name or definite description N in a sentence S may be replaced by a co-denoting name or description M without altering the denotation of S

Assumption (A) allows that an occurrence of a name or a definite description N in a sentence S may be replaced by a name or description M that denotes the same thing without altering the denotation of S. Thus, (2) comes from (1) by (A). (But it is not clear what role, if any, (2) plays in the argument.) (3) comes from (1) by (A); (4) comes from (3) by (B); and (5) comes from (4) by (A). A similar argument can be used to show that all false sentences denote the same thing. A further conclusion, i