When applied to a list of list-tactics [LT1; ... ;LTn], and a goal g,
the tactical EVERY_LT applies each list-tactic in sequence to every
subgoal generated by the previous one. This can be represented as:
If the list-tactic list is empty, the resulting list-tactic has no effect.
EVERY_LT [LT1;...;LTn] = LT1 THEN_LT ... THEN_LT LTn