Description: Define predicate that
determines if some class is a function.
Definition 10.1 of [Quine] p. 65. For
example, the expression
is true once we define cosine (df-cos13514). This is not the
same as defining a specific function's mapping, which is typically done
using the format of cmpt4467 with the maps-to notation (see df-mpt4469 and
df-mpt26227). Contrast this predicate with the
predicates to determine
if some class is a function with a given domain (df-fn5540), a function
with a given domain and codomain (df-f5541), a one-to-one function
(df-f15542), an onto function (df-fo5543), or a one-to-one onto function
(df-f1o5544). For alternate definitions, see dffun25547, dffun35548,
dffun45549, dffun55550, dffun65552, dffun75563, dffun85564, and dffun95565.
(Contributed by NM, 1-Aug-1994.)