Implemented some enhancement requests

src/core/sheerka/services/SheerkaExecute.py

@@ -458,7 +458,7 @@ class SheerkaExecute(BaseService):
 
                     original_items = return_values[:]
                     evaluated_items = []
-                    to_delete = []
+                    to_delete = set()
                     for evaluator in grouped_evaluators[priority]:
                         evaluator.reset()
 
@@ -496,7 +496,7 @@ class SheerkaExecute(BaseService):
                                             continue
 
                                         # otherwise, item will be removed and replaced by result
-                                        to_delete.append(item)
+                                        to_delete.add(item)
                                         if isinstance(result, list):
                                             evaluated_items.extend(result)
                                         elif isinstance(result, ReturnValueConcept):
@@ -525,7 +525,7 @@ class SheerkaExecute(BaseService):
                                     for result in results:
                                         if result.body != BuiltinConcepts.NO_RESULT:
                                             evaluated_items.append(result)
-                                        to_delete.extend(result.parents)
+                                        to_delete.update(result.parents)
                                     sub_context.add_values(return_values=results)
                                 else:
                                     sub_context.add_values(return_values=NO_MATCH)