vardef C.sq(expr n) =
 save p,q;
 picture p; p=nullpicture;
 path q; q=(0,0)--(1,0)--(1,1)--(0,1)--cycle;
 addto p
  if n="Times-Bold": contour q
  else: doublepath q withpen pencircle scaled.0667 fi;
 p scaled (fontsize n/2)
enddef;