How to make pictures using postscript programs (part 13)
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Review of commands:
-all files start with
 %!PS-Adobe-2.0 

-To declare the rectangle in which your pictures is drawn, you need to
 declare the bounding box, with lower left and upper right corner.
 %%BoundingBox: 0.0 0.0 420 420

-For all commands, the arguments come before the command.

-start a new path with
 newpath

-set starting point with
 moveto

-continue path with
 lineto 
 arc     (circular arc counterclockwise)
 arcn    (circular arc clockwise)
 curveto (Bezier curve, needs six arguments)
 rlinet, rmoveto (same as lineto, moveto, but coordinates relative to current)

-use the current path with
 stroke  fill clip

-drawing style and color set with 
 setlinewidth setrgbcolor 

-change coordinate system with
 translate  rotate  scale

-perform arithmetic operations with
 add sub mul div mod neg 

-mathematical functions
 sin cos exp sqrt

-comparison with
 eq le ge

-control structures: loops with
 for

-conditional execution with
 if ifelse

-defining a name to be replaced by something
 def

-use a font
 findfont scalefont setfont

-print a text
 show

-print the page
 showpage