|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 12656). This is not the
same as defining a specific function's mapping, which is typically done
using the format of cmpt 4253 with the maps-to notation (see df-mpt 4255 and
df-mpt2 6072). Contrast this predicate with the
predicates to determine
if some class is a function with a given domain (df-fn 5443), a function
with a given domain and codomain (df-f 5444), a one-to-one function
(df-f1 5445), an onto function (df-fo 5446), or a one-to-one onto function
(df-f1o 5447). For alternate definitions, see dffun2 5450, dffun3 5451,
dffun4 5452, dffun5 5453, dffun6 5455, dffun7 5465, dffun8 5466, and dffun9 5467.
(Contributed by NM, 1-Aug-1994.)|