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-cos13296). This is not the
same as defining a specific function's mapping, which is typically done
using the format of cmpt4325 with the maps-to notation (see df-mpt4327 and
df-mpt26066). Contrast this predicate with the
predicates to determine
if some class is a function with a given domain (df-fn5393), a function
with a given domain and codomain (df-f5394), a one-to-one function
(df-f15395), an onto function (df-fo5396), or a one-to-one onto function
(df-f1o5397). For alternate definitions, see dffun25400, dffun35401,
dffun45402, dffun55403, dffun65405, dffun75416, dffun85417, and dffun95418.
(Contributed by NM, 1-Aug-1994.)