.. _quadrilateral:

quadrilateral figures
=====================

.. index:: figure, square, oblong, rhombus

..

  Of **quadrilateral figures** , 
  
  a **square**  is that which is both equilateral and right-angled; 
  
  an **oblong**  that which is right-angled but not equilateral; 
  
  a **rhombus**  that which is equilateral but not right-angled; 
  
  and a **rhomboid** that which has its opposite sides and angles equal to one
  another but is neither equilateral nor right-angled. 
  
  And let quadrilaterals other than these be called **trapezia**.

  -- Euclid