The main goal of the specialization operators is to exclude some examples incorrectly covered by one rule. This can also lead to the undesirable consequence of excluding some correctly covered examples.
One of the specialization operators used by YAILS is to add one condition to the rule. This condition can be a symbolic one (i.e. tests a symbolic attribute) or numeric.
This operator restricts a numerical interval. Again this can be done in several ways. Examples of restrictions can be found on section 2.4.1 if you read the figure from right to left.This transformations are guided by the goal of excluding the negative values that lie in the present interval (again a conservative but efficient algorithm).