if (a + b) + c = d, then b + c = d + (a ⋅ (-1))

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• b + c = d + (a ⋅ (-1)),

  if a + b = c, then b = c + (a ⋅ (-1))

  • a + (b + c) = d,

    if the following are true:

    • a = b
    • b = c

    then a = c

    • (a + b) + c = d
    • a + (b + c) = (a + b) + c,

      if a = b, then b = a

      • (a + b) + c = a + (b + c), (a + b) + c = a + (b + c)