Generate a YGOPro Lua script for the following Yu-Gi-Oh card effect:
During battle between this attacking card and a Defense Position monster whose DEF is lower than the ATK of this card, inflict the difference as Battle Damage to your opponent.
--未知ガエル
--Submarine Frog
local s,id=GetID()
function s.initial_effect(c)
	--Pierce
	local e1=Effect.CreateEffect(c)
	e1:SetType(EFFECT_TYPE_SINGLE)
	e1:SetCode(EFFECT_PIERCE)
	c:RegisterEffect(e1)
end