def z(x0, y0):
    out = []
    x = (x0 << 1)
    y = (y0 << 1)
    n = 1
    other = lambda t: t ^ (n << 1)
    parent = lambda t: (t | n) & ~(n << 1)
    b = False  # whether some descendant of x is greater than x0
    c = (x == y)
    while n <= x0:
        nx, x, ny, y = other(x), parent(x), other(y), parent(y)
        if c:
            # after x and y meet on their path to the root
            if nx < x:
                out.append(nx)
        elif x == y:
            # they meet for the first time
            if not b:
                out.append(other(nx))
            c = True
        else:
            # x and y have not met yet
            if not b and x < nx:
                b = True
                out.append(other(nx))
            elif b and nx < x:
                out.append(nx)
            out.append(ny)
        n <<= 1
    return sorted(out)