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*Proposition:* The composition of two functions is also a function,.

forallf,g,A,B,C:f:A->B/\g:B->C=>fog:A->C.

*Proof:* see lecture notes (will be discussed later).

*Proposition:* direct characterization of function composition

forallf,g,A,B,C:f:A->B/\g:B->C=>forallxin A: (fog)(x) =g(f(x)).

Author: Wolfgang Schreiner

Last Modification: October 14, 1999