2PLOT: plot polygon - draw polygons

Usage: plot polygon <x1> <y1> <x2> <y2> <x3> <y3> ... (normal mode)
       plot polygon [[<x>] <y1>...]                   (list mode)

Normal mode:
The command draws a polygon with the given edges. At least three
points must be specified.

List mode:
The command draws polygons with the edges given by the vector expressions
x, y1,... If no vector expressions are specified, polygons are drawn
through the points of all list columns. If the x-expression is
omitted (i.e. if only a single expression, y1, is given), the
x-coordinates are taken from the x-column of the list. The number of
list points must be three or more.
