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-cos13142). This is not the
same as defining a specific function's mapping, which is typically done
using the format of cmpt4360 with the maps-to notation (see df-mpt4362 and
df-mpt26072). Contrast this predicate with the
predicates to determine
if some class is a function with a given domain (df-fn5420), a function
with a given domain and codomain (df-f5421), a one-to-one function
(df-f15422), an onto function (df-fo5423), or a one-to-one onto function
(df-f1o5424). For alternate definitions, see dffun25427, dffun35428,
dffun45429, dffun55430, dffun65432, dffun75443, dffun85444, and dffun95445.
(Contributed by NM, 1-Aug-1994.)