Description: Define predicate that
determines if some class is a function.
Definition 10.1 of [Quine] p. 65. For
example, the expression
This math symbol is not active (i.e. was not declared in this scope).
Fun is true once we define cosine (df-cos12724). This is not the
same as defining a specific function's mapping, which is typically done
using the format of cmpt4301 with the maps-to notation (see df-mpt4303 and
df-mpt26134). Contrast this predicate with the
predicates to determine
if some class is a function with a given domain (df-fn5504), a function
with a given domain and codomain (df-f5505), a one-to-one function
(df-f15506), an onto function (df-fo5507), or a one-to-one onto function
(df-f1o5508). For alternate definitions, see dffun25511, dffun35512,
dffun45513, dffun55514, dffun65516, dffun75526, dffun85527, and dffun95528.
(Contributed by NM, 1-Aug-1994.)