protected StackableOperator createHeadOperator(Functor head, Clause clause)
    {
        return new PositionalContextOperator(head, -1, true, true, false, null, contextStack.peek());
    }
protected StackableOperator createHeadOperator(Functor head, Clause clause)
    {
        return new PositionalContextOperator(head, -1, true, true, false, null, contextStack.peek());
    }
protected StackableOperator createHeadOperator ( Functor head , Clause clause ) { return new PositionalContextOperator ( head , - 1 , true , true , false , null , contextStack . peek ( ) ) ; }
{@inheritDoc}
{