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-cos13806). This is not the
same as defining a specific function's mapping, which is typically done
using the format of cmpt4510 with the maps-to notation (see df-mpt4512 and
df-mpt26301). Contrast this predicate with the
predicates to determine
if some class is a function with a given domain (df-fn5596), a function
with a given domain and codomain (df-f5597), a one-to-one function
(df-f15598), an onto function (df-fo5599), or a one-to-one onto function
(df-f1o5600). For alternate definitions, see dffun25603, dffun35604,
dffun45605, dffun55606, dffun65608, dffun75619, dffun85620, and dffun95621.
(Contributed by NM, 1-Aug-1994.)