Two straight lines {anti-parallel line} can cut two straight lines so first angle cut by one line is supplementary to second angle cut by other line.
Line segments {extended line} can be longer, at either end.
Curved lines {isotopic line} can be perpendicular to themselves.
A line {median, trapezoid} joins midpoints of non-parallel trapezium or trapezoid sides.
Figure lines {nodal line} can stay fixed during rotation or deformation.
Lines {oblique line} can be neither parallel nor perpendicular to a direction.
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Date Modified: 2022.0225