When referring to keyboard characters, printing characters are written thus: a, while control characters are written like this: C-a. Thus <C-a> is the character you get by holding down the <CTRL> key while you type c. Finally, the special control characters carriage-return, line-feed and space are often abbreviated to <RET>, <LFD> and <SPC> respectively.
When introducing a built-in predicate, we shall present its usage with a
mode spec which has the form name(arg, ..., arg)
where each
arg denotes how that argument should be instantiated in goals, and
has one of the following forms:
In the context of some directives, we shall need the following notation:
Predicates in Prolog are distinguished by their name and their
arity. The notation name
/
arity is therefore used
when it is necessary to refer to a predicate unambiguously; e.g.
concatenate/3
specifies the predicate which is named
"concatenate" and which takes 3 arguments.
More generaly, a predicate spec may be
name/
arity
[
elem_form,...]
pred_spec1,
pred_spec2
dcg(
pred_spec)