Square. Oblong (long tetragon). Rhombus (helmuain). Rhombus (helmuain).

Of quadrilateral figures, one is called a square. And another an oblong (long tetragon), which is a right-angled figure but is not equilateral. Another is called elmuayn (rhombus), which is equilateral but not right-angled. There is yet another, similar to the almuayn, which has its opposite sides equal and likewise its opposite angles equal, and nevertheless is contained neither by equal sides nor by right angles. And besides those already named, all quadrilateral figures are called elmuariffe, that is, irregular.

Parallels.

Equidistant lines are those which, placed in the same surface and produced on both the one and the other side, do not meet, even were they drawn out to infinity.

The postulates are 5.

1a (Figure)
From each point to any other point the straight line can be drawn, and the defined line can be drawn out continuously and straight as far as one pleases.

2a (Figure)
Upon every center, occupying as much space as one pleases, the circle can be made.

3a (Figure)
All right angles are equal to one another.

4a (Figure)
If a straight line falls upon two straight lines, and the two angles on one side are less than 2 right angles, these 2 lines, produced on that side, will without doubt meet.

5a (Figure)
Two straight lines do not enclose any surface.