Usage:
A1, ... , An; B1, ... , Bm

The predicate ; (or) executes first the left goal A1, ... , An and if it fails or on Next Answer executes the right B1, ... , Bm .

Remark:
The priority of ; (or) is smaller then the priority of comma.

Remark:
In if-then-else predicate you can use ; instead of else (for compatibility with other Prolog compilers).

Example:

?-
  read(X),
  (X<2 ; X>3). % true outside from the interval from two to three