Description: Define predicate that
determines if some class 𝐴 is a function.
Definition 10.1 of [Quine] p. 65. For
example, the expression
Fun I is true (funi 5155). This is not the same as defining a
specific function's mapping, which is typically done using the format of
cmpt 3989 with the maps-to notation (see df-mpt 3991). Contrast this
predicate with the predicates to determine if some class is a function
with a given domain (df-fn 5126), a function with a given domain and
codomain (df-f 5127), a one-to-one function (df-f1 5128), an onto function
(df-fo 5129), or a one-to-one onto function (df-f1o 5130). For alternate
definitions, see dffun2 5133, dffun4 5134, dffun6 5137, dffun7 5150, dffun8 5151,
and dffun9 5152. (Contributed by NM,
1-Aug-1994.) |