Re: How do you return a subclass instance from a base class method?

[Daniel via Digitalmars-d-learn]

```
PosetRelation transitivity(PosetRelation R, PosetRelation S)
{
   // These if conditions are typically ordered from easiest to
   // most involved-to-check.
   if (R.op == S.op &&
       is(typeof(R) == typeof(S)) &&
       R.right == S.left)
   {
      return new typeof(R)(
         R.left, S.right,
         by("transitivity of " ~ R.op));     // Proof by this 
axiom
   }
   return null;
}
```

Not sure if that would work yet.  Have to test it.