An expert module to improve the consistency of analytic hierarchy process matrices

In AHP (Analytic Hierarchy Process), the calculated priorities are plausible only if the comparison matrices are consistent or near consistent. This condition is reached if – within the pairwise comparison process – the transitivity and reciprocity rules are respected. We describe a Prolog application which helps the decision-maker to build a consistent matrix or a matrix with a controlled error. An expert module detects rule transgressions, explains them (How-explanations), suggests alternatives (What If-explanations) and gives hints on how to continue the comparison process.