1. Out-of-plane straight line is parallel to the plane l//α.

2. Parallel Theorem of Intersection Lines (This is not necessarily true) If l//α, l(β, α∪β= a, then L ‖ A.

3. The intersecting lines are parallel. If a//α, b//α, A and b(β, a∩b=P, then α//β.

4. Parallelism Theorem of the Intersection of Parallel Planes (this uncertainty) If α/β, α∪δ= A, β∪δ= B, then a//b/b.