Generate a YGOPro Lua script for the following Yu-Gi-Oh card effect:
Once per turn, during your Standby Phase, if you control no other monsters: Change this card to Defense Position, and if you do, its Battle Position cannot be changed this turn. * The above text is unofficial and describes the card's functionality in the OCG.
--ダークゼブラ
--Dark Zebra
local s,id=GetID()
function s.initial_effect(c)
	--to defense
	local e1=Effect.CreateEffect(c)
	e1:SetDescription(aux.Stringid(id,0))
	e1:SetType(EFFECT_TYPE_FIELD+EFFECT_TYPE_TRIGGER_F)
	e1:SetCategory(CATEGORY_POSITION)
	e1:SetCode(EVENT_PHASE|PHASE_STANDBY)
	e1:SetRange(LOCATION_MZONE)
	e1:SetCountLimit(1)
	e1:SetCondition(s.condition)
	e1:SetTarget(s.target)
	e1:SetOperation(s.operation)
	c:RegisterEffect(e1)
end
function s.condition(e,tp,eg,ep,ev,re,r,rp)
	return tp==Duel.GetTurnPlayer() and Duel.GetFieldGroupCount(tp,LOCATION_MZONE,0)==1
end
function s.target(e,tp,eg,ep,ev,re,r,rp,chk)
	if chk==0 then return true end
	Duel.SetOperationInfo(0,CATEGORY_POSITION,e:GetHandler(),1,0,0)
end
function s.operation(e,tp,eg,ep,ev,re,r,rp)
	local c=e:GetHandler()
	if c:IsRelateToEffect(e) and c:IsPosition(POS_FACEUP_ATTACK) and Duel.ChangePosition(c,POS_FACEUP_DEFENSE)~=0 then
		local e1=Effect.CreateEffect(c)
		e1:SetType(EFFECT_TYPE_SINGLE)
		e1:SetCode(EFFECT_CANNOT_CHANGE_POSITION)
		e1:SetProperty(EFFECT_FLAG_CANNOT_DISABLE+EFFECT_FLAG_COPY_INHERIT)
		e1:SetReset(RESETS_STANDARD_PHASE_END)
		c:RegisterEffect(e1)
	end
end