|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 14640). This is not the
same as defining a specific function's mapping, which is typically done
using the format of cmpt 4643 with the maps-to notation (see df-mpt 4645 and
df-mpt2 6554). Contrast this predicate with the
predicates to determine
if some class is a function with a given domain (df-fn 5807), a function
with a given domain and codomain (df-f 5808), a one-to-one function
(df-f1 5809), an onto function (df-fo 5810), or a one-to-one onto function
(df-f1o 5811). For alternate definitions, see dffun2 5814, dffun3 5815,
dffun4 5816, dffun5 5817, dffun6 5819, dffun7 5830, dffun8 5831, and dffun9 5832.
(Contributed by NM, 1-Aug-1994.)|