ALGO_IT(A,p,r,k)
STQ=STR=LAST=NIL;
CP=P; CR=R;
While(CP<=CR || STR != NILL) do
	if(CP < CR) then
		ret = false
		if (CP = CR) then
			ret = (k==A[CP])
			LAST=CP
			CP=CR+1
		else
			Q=CP+CR/2
			STQ=PUSH(STQ,Q)
			STR=PUSH(STR,CR)
			CR=Q-1
	else
		Q=TOP(STQ); CR=TOP(STR);
	if(LAST != CR)then
		ret = (k==A[q] || val)
		if (ret=(k==A[q]) then
			LAST=CP
			CP=CR+1
			STP=STQ=POP();
		else if(ret=false)then
			CP=Q+1
		else
			LAST=CP
			CP=CR+1
			STP=STQ=POP();
	else
		ret=val
		LAST=CP
		CP=CR+1
		STP=STQ=POP();
	return ret;