==== Modification du symbol ligne de surplomb ====

    def l_overhang (expr P) =
      T:=identity;
      cas := 0;
      dlzka := arclength P;
      mojkrok:=adjust_step(dlzka, 0.3u);
      pickup PenC;
      t1:=0;
      forever:
        t := arctime (cas + mojkrok/5) of P;
        t2 := arctime (cas + mojkrok) of P;
        thfill (subpath (t1,t2) of P) -- 
          ((point t of P) + .3u * unitvector(thdir(P,t) rotated 90)) -- 
          cycle;
        cas := cas + mojkrok;
        exitif cas > dlzka - (2*mojkrok/3); % for rounding errors
        t1:=t2;
      endfor;
      thdraw P;
    enddef;