Futile attempts at improving average runtime

vsp.py

@@ -44,13 +44,19 @@ def has_vsp(model: Model, impfunction: ModelFunction,
     bottom = model.ordering.bottom()
 
     C: Dict[ModelValue, Set[ModelValue]] = {}
-    U: Dict[ModelValue, Set[ModelValue]] = {}
-
-    for d in model.designated_values:
-        C[d] = model_closure({d,}, model.logical_operations, None)
-        U[d] = {y for y in model.designated_values if impfunction(d, y) in model.designated_values}
 
     for x in model.designated_values:
+
+        # Discard ({⊥} ∪ A', B) subalgebras
+        if bottom is not None and x == bottom:
+            continue
+
+        # Discard ({⊤} ∪ A', B) subalgebras when negation is defined
+        if top is not None and negation_defined and x == top:
+            continue
+
+        if x not in C:
+            C[x] = model_closure({x,}, model.logical_operations, None)
         Xs = C[x]
 
         # Discard ({⊥} ∪ A', B) subalgebras
@@ -61,8 +67,26 @@ def has_vsp(model: Model, impfunction: ModelFunction,
         if top is not None and negation_defined and top in Xs:
             continue
 
-        Ux = U[x]
+        for y in model.designated_values - Xs:
-        for y in model.designated_values - Xs - Ux:
+
+            # Discard (A, {⊤} ∪ B') subalgebras
+            if top is not None and y == top:
+                continue
+
+            # Discard (A, {⊥} ∪ B') subalgebras when negation is defined
+            if bottom is not None and negation_defined and y == bottom:
+                continue
+
+            # Discard ({a} ∪ A', {b} ∪ B') subalgebras when a <= b
+            if model.ordering.is_lt(x, y):
+                continue
+
+            # Discard ({a} ∪ A', {b} ∪ B') subalgebras when b <= a and negation is defined
+            if negation_defined and model.ordering.is_lt(y, x):
+                continue
+
+            if y not in C:
+                C[y] = model_closure({y,}, model.logical_operations, None)
             Ys = C[y]
 
             # Discard (A, {⊤} ∪ B') subalgebras