Problem A: [Ivanoff]

  A variable circular arc of constant length, l, 
  has one end fixed in position and direction.
  Find the locus of its other end.


References:

L. S. Johnston;
  An Unusual Spiral,
  AMM 40 (1933) 596

V. F. Ivanoff;
  E 51 (solution by O. J. Ramler)
  AMM 40 (1933) 609