  We present a new approach to the study of multiplier ideals in a local,
two-dimensional setting. Our method allows us to deal with ideals, graded
systems of ideals and plurisubharmonic functions in a unified way. Among the
applications are a formula for the complex integrability exponent of a
plurisubharmonic function in terms of Kiselman numbers, and a proof of the
openness conjecture by Demailly and Kollar. Our technique also yields new
proofs of two recent results: one on the structure of the set of complex
singularity exponents for holomorphic functions; the other by Lipman and
Watanabe on the realization of ideals as multiplier ideals.
