 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, important to Church, is that if, as this argument seems to demonstrate, (1) and (5) denote the same thing, this cannot be the propositions expressed by each, since those are clearly different. (For further discussion see  supplement C.1  as well as the supplement to the entry on  truth values.)