Merge pull request #2748 from ngeiswei/relax-check_evaluatable

Relax check_evaluatable to allow subtypes of concept and predicate

opencog/atoms/core/Checkers.cc

@@ -60,13 +60,13 @@ bool check_evaluatable(const Handle& bool_atom)
 		// Allow conjunction, disjunction and negation of
 		// predicates. Since it cannot inherit from EVALUATABLE_LINK
 		// (cause it's a Node) we have to add it here.
-		if (PREDICATE_NODE == t) continue;
+		if (h->is_type(PREDICATE_NODE)) continue;
 
 		// Allow conjunction, disjunction and negation of concepts as
 		// well, in that case these are interpreted as intersection,
 		// union and complement. Since it cannot inherit from
 		// EVALUATABLE_LINK (cause it's a Node) we have to add it here.
-		if (CONCEPT_NODE == t) continue;
+		if (h->is_type(CONCEPT_NODE)) continue;
 
 		// Fucking quote links. I hate those with a passion.
 		if (QUOTE_LINK == t) continue;