% --- start of displayed preamble in the book --- def square=(unitsquare scaled 5mm) enddef; % --- end of displayed preamble in the book --- defaultfont:="ptmr8r"; warningcheck:=0; beginfig(1) for i=0 upto 4: for j=0 upto 4: draw square shifted (i*6mm,j*6mm); endfor; endfor; endfig; end;