%CORNER CO-ORDINATES
%
%   The CORNER CO-ORDS window gives the x,y co-ordinates
%of the conrners of the function (specifically, of the 
%image of the unit square under the function).  The points
%are labeled 
%(0,1) -> X
%(0,0) -> Y
%(1,0) -> Z
%(1,1) -> W
%The text for the co-ordinates of X,Y, and Z is editable,
%and the user may change their values manually (see
%GENERAL help topic).  The co-ordinates for W are
%displayed, but are not editable, as they are fully
%determined by the co-ordinates of the other three points.
%The co-ordinates shown are those of the "current
%function" (see FCN SELECTION), and are updated whenever
%changes are made with the SQUARE TRANSFORMATION controls
%or on the graphics screen, or the current function is
%changed.  The co-ordinates of these three corners may
%also be changed using the labelled buttons on their
%figures (see GRAPHICS WINDOW).
%   Any function for which any corner co-ordinate is less
%than 0 or greater than 1 is "out of bounds," and the 
%FUNCTION ON box (see FCN SELECTION) will remain "off"
%until the function is brought back "in bounds."