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-cos13203). This is not the
same as defining a specific function's mapping, which is typically done
using the format of cmpt4376 with the maps-to notation (see df-mpt4378 and
df-mpt26108). Contrast this predicate with the
predicates to determine
if some class is a function with a given domain (df-fn5441), a function
with a given domain and codomain (df-f5442), a one-to-one function
(df-f15443), an onto function (df-fo5444), or a one-to-one onto function
(df-f1o5445). For alternate definitions, see dffun25448, dffun35449,
dffun45450, dffun55451, dffun65453, dffun75464, dffun85465, and dffun95466.
(Contributed by NM, 1-Aug-1994.)