"Parallelism of two strings in alternating tangles (revised version)"


abstract
We consider the parallelism of two strings in alternating tangles. We show that if there is a pair of parallel strings in an alternating tangle then its alternating diagrams satify certain conditions. As a corollary, for knots admitting a decomposition into two alternating tangles with two or three strings, we prove that its non-trivial Dehn surgery yields a 3-manifold with essential lamination. Hence they have property P and satisfy the cabling conjecture.