Declarations

A Dusa program is a sequence of declarations. This program has 3 declarations, and we read it as saying that a and b are immediately provable and that a and b together imply c.

# a pound sign followed by a space is a line comment

a.
b.
c :- a, b.

All these declarations are rules. The first two rules have no premises, and the third rule has two premises (a and b), with the conclusion c.