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

Start from the conclusion and work back up the proof. Click the arrow to show the parents.

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

  if the following are true:

  • a = b
  • b = c

  then a = c

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

    if the following are true:

    • a = b + c
    • c = d

    then a = b + d

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