u = 1cm;

beginfig(1)

pickup pencircle scaled 1pt;

draw (-8u, 3u)--(9u, 3u);

pickup pencircle scaled 3pt;

path a, b, c;
a := (-8u, 3u)--(11u, 3u);
b := (-5u, 2u)--((-5u, 2u) shifted (6u, 3u));
c := (-4u, 1u)--((-4u, 1u) shifted (6u, 3u));

pair up, vp;
up := a intersectionpoint b;
vp := a intersectionpoint c;
draw up--vp;

b := ((-5u, 1u) shifted (6u, 3u))--((-5u, 1u) shifted (8u, -1u));
c := ((-4u, 2u) shifted (6u, 3u))--((-4u, 2u) shifted (8u, -1u));

up := a intersectionpoint b;
vp := a intersectionpoint c;
draw up--vp;

pickup pencircle scaled 1pt;

path p;
p :=
  (-4u, 2u)--
  (-5u, 2u)--
  (-5u, 1u)--
  (-4u, 1u)--
  cycle;


draw  p;

draw p shifted (6u, 3u);
draw p shifted ((6u, 3u) + (2u, -4u));

pickup pencircle scaled 0.5pt;

drawarrow (-5u, 2u)--((-5u, 2u) shifted (6u, 3u)) dashed evenly;
drawarrow (-4u, 1u)--((-4u, 1u) shifted (6u, 3u)) dashed evenly;

drawarrow ((-5u, 1u) shifted (6u, 3u))--((-5u, 1u) shifted (8u, -1u)) dashed evenly;
drawarrow ((-4u, 2u) shifted (6u, 3u))--((-4u, 2u) shifted (8u, -1u)) dashed evenly;

endfig;

end