What is Basic objects?

Through two distinct points $A$ and $B$ pass:

• the segment $[AB]$: the part of the line between $A$ and $B$ (it has a length, written $AB$);
• the ray $[AB)$: starts at $A$, goes through $B$ and continues forever;
• the line $(AB)$: extends forever on both sides. Two points determine exactly one line.

Points on the same line are called aligned.