stack = []
def DFS():
        def findpath():
                global pos
                global dest
                global stack
                # This eats O(intersections) stack
                val = valid(neighbours0(pos[0],pos[1]))
                try:
                        val.remove(stack[-1])
                except IndexError:
                        # Should possibly only happen on the first entry
                        pass
                if val:
                        stack.append(pos)
                        for path in val:
                                pos = path
                                search(path)
                                if pos == dest or findpath(): return True
                        pos = stack.pop()
                return False
        findpath()