π π := m ¯ ¯ a D n a = m ¯ ¯ a l b ∇ ∇ b n a , ν ν := m ¯ ¯ a Δ Δ n a = m ¯ ¯ a n b ∇ ∇ b n a , μ μ := m ¯ ¯ a δ δ n a = m ¯ ¯ a m b ∇ ∇ b n a , λ λ := m ¯ ¯ a δ δ ¯ ¯ n a = m ¯ ¯ a m ¯ ¯ b ∇ ∇ b n a ;