|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 12704). This is not the
same as defining a specific function's mapping, which is typically done
using the format of cmpt 4291 with the maps-to notation (see df-mpt 4293 and
df-mpt2 6115). Contrast this predicate with the
predicates to determine
if some class is a function with a given domain (df-fn 5486), a function
with a given domain and codomain (df-f 5487), a one-to-one function
(df-f1 5488), an onto function (df-fo 5489), or a one-to-one onto function
(df-f1o 5490). For alternate definitions, see dffun2 5493, dffun3 5494,
dffun4 5495, dffun5 5496, dffun6 5498, dffun7 5508, dffun8 5509, and dffun9 5510.
(Contributed by NM, 1-Aug-1994.)|