program aequip1a;
var
  x,y:       integer;
  Eps:       real;
  Xl,Yl:     real;
  L:         real;
  P:         real;
  DeltaP:    real;

procedure Pot;
var
  r:     real;
  Dx,Dy: real;
begin
Dx:=x-Xl; Dy:=y-Yl;
r:=sqrt(Dx*Dx+Dy*Dy);
P:=L/r;
end;

procedure Zeichne;
begin
if abs(round(P)-P)<=Eps
  then plot(x,y,1);
end;

begin
Eps:=0.1;
DeltaP:=1;
Xl:=100;
Yl:=100;
L:=1000;


graphmode;
for y:=0 to 63 do
  for x:=0 to 239 do
    begin
    Pot;
    Zeichne;
    end;
delay(40);

repeat
until keypressed

end.