% --- start of displayed preamble in the book --- input boxes % --- end of displayed preamble in the book --- defaultfont:="ptmr8r"; warningcheck:=0; beginfig(1) vardef labelarrow (suffix BoxA,BoxB) expr Line = drawarrow Line cutbefore bpath BoxA cutafter bpath BoxB; point (.5*length Line) of Line enddef; defaultscale:=2; boxjoin(a.e=b.w-(.75in,1.5in)); boxit.one("One"); circleit.two("Two"); drawboxed(one,two); label.lft("1.",one.w); label.rt("2.",two.e); label.top("a.",labelarrow(one,two) one.c{dir90}..tension0.8..{dir90}two.s); endfig; end;