beginfig(1)
  u:=1cm;
  pair A,B,C,D,E,F,G,H,I;
  A := (4u,0);
  B := (2u,-u);
  C := (2u,u);
  D := (0,0);
  E := (-u,-u);
  F := (-u,u);
  G := (-u,0);
  H := (-2u,0);
  I := (-3u,0);
  draw A--B; draw A--C; draw A--D;
  draw B--C; draw B--D; draw C--D;
  draw E--D; draw D--F; draw D--G;
  draw G--H; draw H--I;
  dotlabel.top(btex $1$ etex, A);
  dotlabel.bot(btex $2$ etex, B);
  dotlabel.top(btex $3$ etex, C);
  dotlabel.bot(btex $4$ etex, D);
  dotlabel.bot(btex $5$ etex, E);
  dotlabel.bot(btex $6$ etex, F);
  dotlabel.bot(btex $7$ etex, G);
  dotlabel.bot(btex $8$ etex, H);
  dotlabel.bot(btex $9$ etex, I);
endfig;