Embedding tangles in links
  We reprove and extend a result of David Krebes (J. Knot Theory Ramif. 8 (1999), 321-352) giving an obstruction to embedding a tangle T into a link L. Closing the tangle up in the two obvious ways gives rise to two links, the numerator and denominator links n(T) and d(T). Applying a homological argument to the 2-fold branched covers of these links, we show that the gcd of the determinants of the numerator and denominator divides the determinant of L. 
Daniel Ruberman