|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 11589). This is not the
same as defining a specific function's mapping, which is typically done
using the format of cmpt 3684 with the maps-to notation (see df-mpt 3686 and
df-mpt2 5409). Contrast this predicate with the
predicates to determine
if some class is a function with a given domain (df-fn 4323), a function
with a given domain and codomain (df-f 4324), a one-to-one function
(df-f1 4325), an onto function (df-fo 4326), or a one-to-one onto function
(df-f1o 4327). For alternate definitions, see dffun2 4839, dffun3 4840,
dffun4 4841, dffun5 4842, dffun6 4844, dffun7 4854, dffun8 4855, and dffun9 4856.
(Contributed by NM, 1-Aug-1994.)|