To prove that AB is parallel to CD (AB||CD), where EF is a Transversal Line (the line that cuts across 2 other lines), we can use the help of following types of angles:

Corresponding Angles:

m=q | n=r | o=s | p=t

Alternate Interior Angles:

r=p | q=o

Alternate Exterior Angles:

t=n | s=m

Supplementary Angles:

r + o = 180° | q + p = 180°

Vertically Opposite Angles:

m=o | n=p | q=s | r=t

Moreover, since AB, CD & EF are straight lines, so:

m + n = 180° | n + o = 180° | o + p = 180° | p + m = 180°

q + r = 180° | r + s = 180° | s + t = 180° | t + q = 180°