How can you prove that a constructed line is parallel to a given line? assume that the transversal line is not perpendicular to the other lines?

Assuming that no transversal line is present, I can present only the statements base on the figures of a parallelogram. A parallelogram is a quadrilateral. They only differ on the number of their parallel sides. A square has 2 parallel sides and all of its sides are equal or the same. A rhombus has 2 parallel sides and all of its sides are equal or only two of its sides are equal. A rectangle has 2 parallel sides. One parallel side is the same and can be bigger or smaller than the other parallel side. Trapezoid has only one pair of parallel sides. The other pair is a mirror to the other.