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% --- end of displayed preamble in the book ---
% graphic converted to gray in book using 'color2gray'
defaultfont:="ptmr8r";
warningcheck:=0;
beginfig(1)
numeric u;
u=5mm;
path p[];
p1=fullcircle scaled 5u;
p2=unitsquare scaled 3u shifted (0,5u);
draw p2;
draw p1 withcolor red;
draw interpath(.1,p1,p2) withcolor .25[red,green];
draw interpath(.25,p1,p2) withcolor .5[red,green];
draw interpath(.5,p1,p2) withcolor green;
draw interpath(.75,p1,p2) withcolor .5[green,black];
draw interpath(.9,p1,p2) withcolor .7[green,black];
endfig;
end;