Update

line.md

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 # Line
 
-Line is one of the most basic geometric shapes, it is straight, continuous, [infinitely](infinity.md) long and infinitely thin. A finite continuous part of a line is called **line segment**, though in practice we sometimes call line segments also just *lines*. In flat, non-curved geometries shortest path between any two points always lies on a line.
+Line is one of the most basic geometric shapes, it is straight, continuous, [infinitely](infinity.md) long and infinitely thin. A finite continuous part of a line is called **line segment**, though in practice we sometimes call line segments also just *lines*. Considering normal, finite dimensional non-curved space/geometry without any obstacles etc., the shortest path between any two distinct points always lies on a line, which is also the only line that goes through both of these points.
 
 Line is a one [dimensional](dimension.md) shape, i.e. any of its points can be directly identified by a single number -- the signed distance from a certain point on the line. But of course a line itself may exist in more than one dimensional spaces (just as a two dimensional sheet of paper can exist in our three dimensional space etc.).
 
@@ -149,4 +149,6 @@ To add [antialiasing](antialiasing.md) here you wouldn't just draw one pixel at
 
 - [curve](curve.md)
 - [vector](vector.md)
-- [plane](plane.md)
+- [plane](plane.md)
+- [circle](circle.md)
+- [shape](shape.md)