Proof: Manipulation 2

Let's prove the following theorem:

(a ⋅ (b ⋅ (-1))) ⋅ 2 = (ab) ⋅ (-2)

Proof:

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Proof Table
# Claim Reason
1 (ab) ⋅ (-1) = a ⋅ (b ⋅ (-1)) (ab) ⋅ (-1) = a ⋅ (b ⋅ (-1))
2 ((ab) ⋅ (-1)) ⋅ 2 = (a ⋅ (b ⋅ (-1))) ⋅ 2 if (ab) ⋅ (-1) = a ⋅ (b ⋅ (-1)), then ((ab) ⋅ (-1)) ⋅ 2 = (a ⋅ (b ⋅ (-1))) ⋅ 2
3 ((ab) ⋅ (-1)) ⋅ 2 = (ab) ⋅ ((-1) ⋅ 2) ((ab) ⋅ (-1)) ⋅ 2 = (ab) ⋅ ((-1) ⋅ 2)
4 (-1) ⋅ 2 = -2 (-1) ⋅ 2 = -2
5 (ab) ⋅ ((-1) ⋅ 2) = (ab) ⋅ (-2) if (-1) ⋅ 2 = -2, then (ab) ⋅ ((-1) ⋅ 2) = (ab) ⋅ (-2)
6 ((ab) ⋅ (-1)) ⋅ 2 = (ab) ⋅ (-2) if ((ab) ⋅ (-1)) ⋅ 2 = (ab) ⋅ ((-1) ⋅ 2) and (ab) ⋅ ((-1) ⋅ 2) = (ab) ⋅ (-2), then ((ab) ⋅ (-1)) ⋅ 2 = (ab) ⋅ (-2)
7 (a ⋅ (b ⋅ (-1))) ⋅ 2 = (ab) ⋅ (-2) if ((ab) ⋅ (-1)) ⋅ 2 = (a ⋅ (b ⋅ (-1))) ⋅ 2 and ((ab) ⋅ (-1)) ⋅ 2 = (ab) ⋅ (-2), then (a ⋅ (b ⋅ (-1))) ⋅ 2 = (ab) ⋅ (-2)
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