Generation of superfluous Y-atoms

[LBonassi95]

The function "predicates" of predicates visitor creates superfluous quoted "Y()" atoms.

for example, the compilation of formula "O(a & Y(O(b & Y(O(c)))))" should yield the atoms:

• 'Y-Oa-and-YOb-and-YOc'
• 'Y-Ob-and-YOc'
• 'Y-Oc'

Instead, the function predicates(O(a & Y(O(b & Y(O(c)))))) returns:

• 'Y-Oa-and-YOb-and-YOc'
• 'Y-Ob-and-YOc'
• 'Y-Oc'
• 'YOc'
• 'YOb-and-YOc'

This issue will be solved in the branch fix/pddl-predicates-collision