I'm pretty sure the more recent, higher-end RPN calculators have lots more than 4 stack slots. 4 is usually enough in practice anyway. Your example is artific

I'm pretty sure the more recent, higher-end RPN calculators have lots more than 4 stack slots. 4 is usually enough in practice anyway. Your example is artificial. Besides, are you sure your infix calculator will accept this deep a nesting of parentheses? The TI models that were contemporary with the early HPs certainly wouldn't!