def maximiser(f, is_variable, values):
    m = 0
    for i in range(MAX_ITER):
        values = [variation(x) if is_variable[i] else x for i,x in enumerate(initial_values)]
        m = max(m, f(values))
    return m

maximiser(lambda x, y: x * y - x - y, (true, false), (0, 0))