Axial Couple
Two triangles Δabc and Δa'b'c' are said to be an axial couple if
• Δabc and Δa'b'c' are couple
• points ab∩a'b', bc∩b'c', ca∩c'a' are collinear.
The line of collinearity is called axis of the couple.
Two triangles which are perspective from a line is called axial couple