Fix faulty not a proper subset test

S03-operators/mix.t

@@ -174,7 +174,7 @@ ok mix(my @large_arr = ("a"...*)[^50000]), "... a large array goes into a bar -
     ok $bub ⊆ $buper, "⊆ - {$bub.gist} is a submix of {$buper.gist}";
     ok $buper ⊈ $bub, "⊈ - {$buper.gist} is not a submix of {$bub.gist}";
     ok $bub ⊃ $b, "⊃ - {$bub.gist} is a strict supermix of {$b.gist}";
-    ok $buper ⊅ $bub, "⊅ - {$buper.gist} is not a strict supermix of {$bub.gist}";
+    nok $buper ⊅ $bub, "⊅ - {$buper.gist} is not a strict supermix of {$bub.gist}";
     ok $buper ⊇ $bub, "⊇ - {$buper.gist} is a supermix of {$bub.gist}";
     ok $bub ⊉ $buper, "⊉ - {$bub.gist} is not a supermix of {$buper.gist}";
     ok $b (<) $bub, "(<) - {$b.gist} is a strict submix of {$bub.gist} (texas)";