|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 12614). This is not the
same as defining a specific function's mapping, which is typically done
using the format of cmpt 4221 with the maps-to notation (see df-mpt 4223 and
df-mpt2 6039). Contrast this predicate with the
predicates to determine
if some class is a function with a given domain (df-fn 5411), a function
with a given domain and codomain (df-f 5412), a one-to-one function
(df-f1 5413), an onto function (df-fo 5414), or a one-to-one onto function
(df-f1o 5415). For alternate definitions, see dffun2 5418, dffun3 5419,
dffun4 5420, dffun5 5421, dffun6 5423, dffun7 5433, dffun8 5434, and dffun9 5435.
(Contributed by NM, 1-Aug-1994.)|