Algo(T,x,y)
curr=T last=null next=null
Stack S=null Sy=null Sx=null Svol=null Sa=null

while(curr!=null OR S!=null)do
	if curr!=null then
		a=1
		b=1
		val=curr->key
		Push(Sval,val)
		if x <= val <= y then
			next=curr->sx
			Push(S,curr)
			Push(Sy,y)
			y=val-1
		else
			next=null
			a=0
	else
		curr=Top(S)
		y=Top(Sy)
		val=Top(Sval)
		if curr->dx != null AND curr->dx != last then
			next=curr->dx
			a=ret
			if a != 0 then
				Push(Sa,a)
				Push(Sx,x)
				x=val+1
		else
			if curr->dx != null then
				b=ret
			else
				b=1
		a=Top(Sa)
		x=Top(Sx)
		ret=a && b
		Pop(S, Sa, Sy, Sx, Sval)
	last=curr
	curr=next
return ret