27.11.11  Checking whether an object in space is a right triangle or a rectangle

See Section 26.15.7 for checking for right triangles and rectangles in 2D geometry.

The is_rectangle command determines whether or not a geometric object is an rectangle or a right triangle.

• is_rectangle takes G, a geometric object or a sequence of three or four points assumed to be the vertices of a triangle or a quadrilateral.
• is_rectangle(G) returns:
  • (for triangle G) 1,2 or 3 if G is a right triangle (the number indicates which vertex is has the right angle).
  • (for quadrilaterals G) 1 if G is a rectangle but not a square.
  • (for quadrilaterals G) 2 if G is square.
  • 0 otherwise.

Examples