|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 12354). This is not the
same as defining a specific function's mapping, which is typically done
using the format of cmpt 4079 with the maps-to notation (see df-mpt 4081 and
df-mpt2 5865). Contrast this predicate with the
predicates to determine
if some class is a function with a given domain (df-fn 5260), a function
with a given domain and codomain (df-f 5261), a one-to-one function
(df-f1 5262), an onto function (df-fo 5263), or a one-to-one onto function
(df-f1o 5264). For alternate definitions, see dffun2 5267, dffun3 5268,
dffun4 5269, dffun5 5270, dffun6 5272, dffun7 5282, dffun8 5283, and dffun9 5284.
(Contributed by NM, 1-Aug-1994.)|