A knowledge unit R is considered as a combination of disjunctive and conjunctive propositions as one knows how to map a complex rule into a simple expression with no redundancy propositions [hZDZ92].

is an atomic premise, and is expressed by a necessity degree given to the premise , followed by a realization degree of the premise(CF).

The knowledge unit R is carried out, if at least one of its disjunctive proposition  is performed. For the learning stage, the net learns how each disjunctive proposition and its negation are.

Learning R consists in the following process:

• when inputs are in the context of R, the output is set to the maximum value of realization of the rule,
• when inputs are in a wrong context of R, the output is set to the minimum value of realization of the rule ,
• and intermediate values are outputs for intermediate situations [Zah92][hZDZ92].

For example:

IF ``favourable context" THEN (A: very necessary AND B: totally necessary) OR (C: somehow forbidden AND D: totally forbidden)

This rule is defined by four atomic propositions (A, B, C, D):

• the expressions "very necessary" and "totally necessary" may be understood as the frequency to be in the context of A (resp. B),
• "very necessary" means that about 80% of favourable contexts are in the context of the premise A,
• "totally necessary" means that 100% of them are in the context of the premise B.

The same reasoning is done with C: ``somehow forbidden'' and D: ``totally forbidden''.