code: def _dihed_cos_low(a, b, c, deriv):
      
      a = Vector3(9, deriv, a, (0, 1, 2))
      b = Vector3(9, deriv, b, (3, 4, 5))
      c = Vector3(9, deriv, c, (6, 7, 8))
      b /= b.norm()
      tmp = b.copy()
      tmp *= dot(a, b)
      a -= tmp
      tmp = b.copy()
      tmp *= dot(c, b)
      c -= tmp
      a /= a.norm()
      c /= c.norm()
      return dot(a, c).results()
docs: Similar to dihed_cos, but with relative vectors