switch_axes(0);
  xyztrange(-10.0,1.0,-7.0,1.0,-10.0,10.0,-1.0,6.0,-10.0,1.0,-7.0,1.0,0); 
  p:=element(0..5);
  h:=2;
  l:=8;
  f:=l+5;
  j:=element(1..3);
  segment(-l-h*i,-l);
  segment(-h*i,-0);
  y:=-sqrt((x^2*(l+x)^2*j^2)/(p^2*l^2-j^2*x^2));
  m:=max(-l,-p*l/j);
  //z:=derive(y,x);
  //ym:=subst(y,x=m);
  //c:=romberg(sqrt(1+z^2),x,m,0);
  //couleur(segment(m-0.1+i*ym,m-0.1+i*(ym+c-f)),2);
  plotfunc(y,x,m,0);
  a:=element(-l..0);
  b:=-sqrt((a^2*(l+a)^2*j^2)/(p^2*l^2-j^2*a^2));
  A:=point(a,b);
  couleur(segment(A,0),2);
  couleur(segment(A,-l),2);
  ap:=sqrt((l+a)^2+b^2);
  ao:=sqrt(a^2+b^2);
  c:=ao+ap;
  //dessin des forces
  couleur(segment(A,a+(b-j)*i),1);
  couleur(segment(A,A+(-l-a-b*i)*p/sqrt((l+a)^2+b^2)),1); 
  couleur(segment(A,A+(l+a+b*i)*p/sqrt((l+a)^2+b^2)+j*i),1); 
  couleur(segment(A,A+(-l-a-b*i)*p/sqrt((l+a)^2+b^2)-j*i),4);
  cercle(-l,0.2);
  if (c<f){
  [couleur(segment(-l-0.1,-l-0.1+i*(c-f)),2),couleur( segment(-l+i*(c-f),-l+i*(c-f-p/10)),1),couleur( segment(-l-0.2+i*(c-f),-l-0.2+i*(c-f-p/10)),1),couleur( segment(-l-0.2+i*(c-f),-l+i*(c-f)),1),couleur( segment(-l-0.2+i*(c-f-p/10),-l+i*(c-f-p/10)),1)];
  };