Generalizations of the Hanoi Towers Problem
  Our theme bases on the classical Hanoi Towers Problem. In this paper we will define a new problem, permitting some positions, that were not legal in the classical problem. Our goal is to find an optimal (shortest possible) sequence of discs' moves. Besides that, we will research all versions of 3-pegs classical problem with some special constraints, when some types of moves are disallowed. 
Sergey Benditkis, Illya Safro