|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-cos 12368). This is not the
same as defining a specific function's mapping, which is typically done
using the format of cmpt 4093 with the maps-to notation (see df-mpt 4095 and
df-mpt2 5879). Contrast this predicate with the
predicates to determine
if some class is a function with a given domain (df-fn 5274), a function
with a given domain and codomain (df-f 5275), a one-to-one function
(df-f1 5276), an onto function (df-fo 5277), or a one-to-one onto function
(df-f1o 5278). For alternate definitions, see dffun2 5281, dffun3 5282,
dffun4 5283, dffun5 5284, dffun6 5286, dffun7 5296, dffun8 5297, and dffun9 5298.
(Contributed by NM, 1-Aug-1994.)|