  In recent years, adaptive learning systems rely increasingly on learning
hierarchy to customize the educational logic developed in their courses. Most
approaches do not consider that the relationships of prerequisites between the
skills are fuzzy relationships. In this article, we describe a new approach of
a practical application of fuzzy logic techniques to the construction of
learning hierarchies. For this, we use a learning hierarchy predefined by one
or more experts of a specific field. However, the relationships of
prerequisites between the skills in the learning hierarchy are not definitive
and they are fuzzy relationships. Indeed, we measure relevance degree of all
relationships existing in this learning hierarchy and we try to answer to the
following question: Is the relationships of prerequisites predefined in initial
learning hierarchy are correctly established or not?
