2.4 What is a rule?

A rule is a formula of the following form: A B.
A is called the antecedent of the rule.
B is called the consequent of the rule.
A and B can be predicate conjunctions.
A can be omitted. In this case, the rule is said to be atomic.
A rule can be:

Rules, contrary to hypotheses and goals, contain wildcards. A wildcard is a variable, which can take any value (literal, expression, ...) If it is assigned a value, it is said to be instantiated. A wildcard is represented by a letter of the alphabet: thus no more than 52 wildcards can appear inside a rule (lower case and upper case letters).