def Hx2Rh(Hx):
    """needs doc string"""
    Rh = [0, 0, 0]
    itk = -Hx[0] + Hx[1] + Hx[2]
    if itk % 3 != 0:
        return 0
    else:
        Rh[1] = itk // 3
        Rh[0] = Rh[1] + Hx[0]
        Rh[2] = Rh[1] - Hx[1]
        if Rh[0] < 0:
            for i in range(3):
                Rh[i] = -Rh[i]
        return Rh
