(b ⋅ a) + ((a ⋅ b) ⋅ (-1)) = 0

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• (b ⋅ a) + ((a ⋅ b) ⋅ (-1)) = 0,

  if a = b, then a + (b ⋅ (-1)) = 0

  • b ⋅ a = a ⋅ b, a ⋅ b = b ⋅ a