|Description: Define predicate that
determines if some class 𝐴 is a function.
Definition 10.1 of [Quine] p. 65. For
example, the expression
Fun cos is true once we define cosine (df-cos 12793). This is not the
same as defining a specific function's mapping, which is typically done
using the format of cmpt 4351 with the maps-to notation (see df-mpt 4353 and
df-mpt2 6186). Contrast this predicate with the
predicates to determine
if some class is a function with a given domain (df-fn 5556), a function
with a given domain and codomain (df-f 5557), a one-to-one function
(df-f1 5558), an onto function (df-fo 5559), or a one-to-one onto function
(df-f1o 5560). For alternate definitions, see dffun2 5563, dffun3 5564,
dffun4 5565, dffun5 5566, dffun6 5568, dffun7 5578, dffun8 5579, and dffun9 5580.
(Contributed by NM, 1-Aug-1994.)|