Description: Define predicate that
determines if some class is a function.
Definition 10.1 of [Quine] p. 65. For
example, the expression
is true (funi 5163). This is not the same as defining a
specific function's mapping, which is typically done using the format of
cmpt 3997 with the maps-to notation (see df-mpt 3999). Contrast this
predicate with the predicates to determine if some class is a function
with a given domain (df-fn 5134), a function with a given domain and
codomain (df-f 5135), a one-to-one function (df-f1 5136), an onto function
(df-fo 5137), or a one-to-one onto function (df-f1o 5138). For alternate
definitions, see dffun2 5141, dffun4 5142, dffun6 5145, dffun7 5158, dffun8 5159,
and dffun9 5160. (Contributed by NM,
1-Aug-1994.) |