@figure;
  O = point( -2.37 , 0 );
  cerayO4 = cerclerayon( O , 4 );
  H = pointsur( cerayO4 , 99.95 )  { noir , rond2 , (-0.6,-0.97) };
  sOH = segment( O , H );
  d = perpendiculaire( H , sOH )  { noir , q2 };