Parallel Lines
Parallel lines are coplanar lines that do not intersect.
Intersecting Lines
Intersecting lines are coplanar and have exactly one point in common.
Oblique Lines
Lines are oblique if they intersect and do not form right angles.
Skew Lines
Two lines are skew if they do not lie in the same plane and never intersect.
Thm. 3.1 transitivity of parallel lines
If two lines are parallel to the same line, then they are parallel to each other.
Thm. 3.2 property of perpendicular lines
If two coplanar lines are perpendicular to the same line, then they are parallel to each other.