Supplementary angles that are not a linear pair

In this photo of a movable stair case there are two angles that are supplementary but not linear pairs. For two angles to be supplementary their measure must add up to 180 degrees. For the the two angles not to be a linear pair they must not share the same vertex and cannot share a side. Angle 1 and angle 2 are supplementary because of the Consecutive Interior Angle Theorem. Consecutive Interior Angle Theorem can apply in this case because lines 3 and 4 or the vertical pipe supports are parallel and a diagonal pipe or transversal (colored red) connects lines 3 and 4. Moveable staircases are used by individuals to complete tasks at a higher level than the base of the stair case.  Moveable stairs are used at Home Depot, libraries, airports and sailing venues to place objects at high levels.

This picture was taken at Annapolis Yacth Club when I was sailing on Sunday.