handle temporal copula reversibility -- can alternatively be handled …

…by introducing a new theorem

pynars/NARS/Control/Reasoner.py

@@ -671,14 +671,21 @@ def inference_step(self, concept: Concept):
                         order_mark = Copula.RetrospectiveImplication
 
                 stamp = Stamp_merge(stamp_task, stamp_belief, order_mark)
+
+                def add_task(term):
+                    sentence_derived = Judgement(term, stamp, truth)
+                    # print(stamp.tense == sentence_derived.stamp.tense)
+                    task_derived = Task(sentence_derived, budget)
+                    # print(task_derived.sentence.tense, task_derived)
+                    # normalize the variable indices
+                    task_derived.term._normalize_variables()
+                    tasks_derived.append(task_derived)
 
-                sentence_derived = Judgement(conclusion, stamp, truth)
-                # print(stamp.tense == sentence_derived.stamp.tense)
-                task_derived = Task(sentence_derived, budget)
-                # print(task_derived.sentence.tense, task_derived)
-                # normalize the variable indices
-                task_derived.term._normalize_variables()
-                tasks_derived.append(task_derived)
+                add_task(conclusion)
+
+                if type(conclusion) is Statement: # TODO: handle this better
+                    if conclusion.is_predictive or conclusion.is_retrospective:
+                        add_task(conclusion.temporal_swapped())
 
             if term_link is not None:
                 for derived_task in tasks_derived: 

pynars/NARS/InferenceEngine/KanrenEngine/nal-rules.yml

@@ -243,3 +243,5 @@ theorems: |
   <(&/, S1, N1, S2) <=> <S2 =\> (&/, S1, N1)>>
   <(&/, S1, N1, S2) <=> <S1 =/> S2>>
   <(&/, S1, N1, <S2 ==> S3>) <=> <(&/, S1, N1, S2) =/> S3>>
+
+  # <<A =/> B> <=> <B =\> A>>

pynars/Narsese/_py/Copula.py

@@ -85,6 +85,14 @@ def get_retrospective(self):
         else:
             return self
 
+    @property
+    def get_temporal_swapped(self):
+        if self == Copula.PredictiveImplication:
+            return Copula.RetrospectiveImplication
+        if self == Copula.RetrospectiveImplication:
+            return Copula.PredictiveImplication
+        return self
+
     def symmetrize(self):
         if self is Copula.Inheritance:
             return Copula.Similarity

pynars/Narsese/_py/Statement.py

@@ -164,6 +164,11 @@ def predictive(self):
     def retrospective(self):
         return Statement(self.subject, self.copula.get_retrospective, self.predicate)
 
+    def temporal_swapped(self):
+        if self.copula is Copula.PredictiveEquivalence:
+            return self # TODO: could be handled by introducing <\> copula
+        return Statement(self.predicate, self.copula.get_temporal_swapped, self.subject)
+
     def clone(self):
         if not self.has_var: return self
         # now, not self.has_var