Move anticipate next index 1 in operation._combine to operation.chain

[ajkerr0]

_combine doesn't need that functionality and makes the function less self-contained. That check can simply be in operation[_plus].chain (since that's the only situation in which it would be needed)

[ajkerr0]

My hesitation is that that short little calculation requires understanding how _combine works. If they are in the same module I guess its no big deal. After all I assume how other things work across the package all the time.