code: public boolean isDerivation(Type parent, Type child) {
  		if (child.equals(parent)) {
  			return true;
  		} else if (child instanceof Type.Nominal) {
  			Type.Nominal t = (Type.Nominal) child;
  			Decl.Type decl = t.getLink().getTarget();
  			return isDerivation(parent, decl.getType());
  		} else {
  			return false;
  		}
  	}
docs: Check whether one type is a derivation of another. For example, in this
  scenario:
  
  <pre>
  type parent is (int p) where ...
  type child is (parent c) where ...
  </pre>
  
  @param parent
  The type being derived to
  @param child
  The type we are trying to derive
  @return