Prolog predicates can be given the role of arithmetic function. The
last argument is used to return the result, the arguments before the
last are the inputs. Arithmetic functions are added using the predicate arithmetic_function/1,
which takes the head as its argument. Arithmetic functions are module
sensitive, that is they are only visible from the module in which the
function is defined and declared. Global arithmetic functions should be
defined and registered from module `user`

. Global definitions
can be overruled locally in modules. The built-in functions described
above can be redefined as well.

**arithmetic_function**(`+Head`)-
Register a Prolog predicate as an arithmetic function (see is/2,
>/2, etc.). The Prolog
predicate should have one more argument than specified by
`Head`, which it either a term`Name/Arity`, an atom or a complex term. This last argument is an unbound variable at call time and should be instantiated to an integer or floating point number. The other arguments are the parameters. This predicate is module sensitive and will declare the arithmetic function only for the context module, unless declared from module`user`

. Example:1 ?- [user]. :- arithmetic_function(mean/2). mean(A, B, C) :- C is (A+B)/2. user compiled, 0.07 sec, 440 bytes. Yes 2 ?- A is mean(4, 5). A = 4.500000

**current_arithmetic_function**(`?Head`)-
Successively unifies all arithmetic functions that are visible from the
context module with
`Head`.