State the property that is used each of the following statements ?

- If a || b, then ∠ 1 = ∠ 5.
- If ∠ 4 = ∠ 6, then a || b.
- If ∠ 4 + ∠ 5 = 180°, then a || b.

State the property that is used each of the following statements ?

- If a || b, then ∠ 1 = ∠ 5.
- If ∠ 4 = ∠ 6, then a || b.
- If ∠ 4 + ∠ 5 = 180°, then a || b.