A line segment has no length.

Every ray has a finite length.

The ray $\overrightarrow{\mathrm{AB}}$ is the same as the ray $\overrightarrow{\mathrm{BA}}$.

The line segment $\overline{\mathrm{AB}}$ is the same as the line segment $\overline{\mathrm{BA}}$.

The line $\overleftrightarrow{\mathrm{AB}}$ is the same as the line $\overleftrightarrow{\mathrm{BA}}$.

Two points $\mathrm{A}$ and $\mathrm{B}$ in a plane determine a unique line segment.

Two intersecting lines intersect at a point.

Two intersecting planes intersect at a point.

If points $\mathrm{A}, \mathrm{B}, \mathrm{C}$ are collinear and points $\mathrm{C}, \mathrm{D}, \mathrm{E}$ are collinear then the points $\mathrm{A},\mathrm{B},\mathrm{C},\mathrm{D},\mathrm{E}$ are collinear.