% --- start of displayed preamble in the book --- input expressg % --- end of displayed preamble in the book --- defaultfont:="ptmr8r"; warningcheck:=0; beginfig(1) z1=(0,0); drawLEVENT(1, 2cm, 1cm)(btex levent etex); z2=(0,-2cm); drawGEVENT(2, 2cm, 1cm)(btex gevent etex); endfig; end;