--- Notice that there is no case
--- ruleCantMatch (Just n1 : ts) (Nothing : as) = True
--- Reason: a local variable 'v' in the actuals might
--- have an unfolding which is a global.
--- This quite often happens with case scrutinees.
+-- Notice that [_$_]
+-- ruleCantMatch [Nothing] [Just n2] = False
+-- Reason: a template variable can be instantiated by a constant
+-- Also:
+-- ruleCantMatch [Just n1] [Nothing] = False
+-- Reason: a local variable 'v' in the actuals might [_$_]
+