CONST Radius = 10;

PROC MoveBallFrame(a, b, dur, t) IS 
  SAVE PS IN 
    Circle.DrawR((t / dur, 0) REL (a, b), 
                 Radius); 
    PS.SetColor(Color.Red); 
    PS.Fill() 
  END 
END;

PROC an := MoveBall(a, b, dur) IS 
  an := 
    (CLOSE(MoveBallFrame, a, b, dur), dur) 
END;

PROC an := CoExtend(a1, a2) IS 
  IF 
    CDR(a1) < CDR(a2) -> 
      a1 := Anim.Extend(a1, CDR(a2)) 
  | CDR(a1) > CDR(a2) -> 
      a2 := Anim.Extend(a2, CDR(a1)) | SKIP 
  FI; 
  an := Anim.Co(a1, a2) 
END;

PROC DrawExtended(an, t) IS 
  APPLY(CAR(an), MIN(CDR(an), t)) 
END;

PROC CoExtendFrame(a1, a2, t) IS 
  DrawExtended(a1, t); DrawExtended(a2, t) 
END;

PROC an := CoExtend2(a1, a2) IS 
  an := 
    (CLOSE(CoExtendFrame, a1, a2), 
     MAX(CDR(a1), CDR(a2))) 
END;

PROC Cmd0() IS 
  IF 
    VAR 
      a ~ (-65.89, 120.6), b ~ (-71.19, -30.34), an1, an2, 
      c ~ (41.66, -41.72) 
    IN 
      an1 := MoveBall(a, b, 1); 
      an2 := MoveBall(a, c, 1); 
      Anim.Play(Anim.Co(Anim.Extend(an1, 1.5), 
                        Anim.Seq(Anim.Skip(0.5), an2))) 
    END 
  FI 
END;