#include <stdio.h>

#define TRUE 1
#define FALSE 0

typedef int BOOLEAN;

typedef struct CELL *LIST;
struct CELL {
	int element;
	LIST next;
};

BOOLEAN lookup(int x, LIST L)
{
	if (L == NULL)
		return FALSE;
	else if (x > L->element)
		return lookup(x, L->next);
	else if (x == L->element)
		return TRUE;
	else /* here x < L->element, and so x could not be
			on the sorted list L */
		return FALSE;
}