On the colength of fractional ideals

The main goal of this paper is to give a recursive formula for the colength of a fractional ideal in terms of some maximal points of its value set and of its projections. The fractional ideals are relative to a class of rings called admissible, a more general class of one dimensional local rings that contains those of algebroid curves. For fractional ideals of such rings with two or three minimal primes, a closed formula for the colength is provided.