a1 Mathematics Department, University of British Columbia, 121-1984 Mathematics Road, Vancouver, Canada V6T 1Y4 and Warsaw University, Poland
The local change in an oriented link diagram which replaces by k positive half-twists is called a tk move. For k even, the local change replacing by is called a tk move. For an unoriented diagram define a k-move, replacing by for any k. The following conjecture was stated in  and .
(Received April 16 1989)
(Revised September 18 1989)