A modified version of Bell's Boolean matrix method for the computation of linear precedence functions associated with a conflict-free matrix of precedence relations is given. This algorithm not only detects when the precedence functions do not exist, but also provides an indication of why they do not exist, so that corrective action can be taken if possible. Necessary and sufficient conditions for the existence of precedence functions are given. The use of Boolean matrices to prove the existence of precedence functions associated with classes of conflict-free grammars is illustrated through an example.
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