  A two-parameter field theoretical representation is given of a 2-dimensional
dirty d-wave superconductor that interpolates between the Gaussian limit of
uncorrelated weak disorder and the unitary limit of a dilute concentration of
resonant scatterers. It is argued that a duality holds between these two
regimes from which follows that a linearly vanishing density of states in the
Gaussian limit transforms into a diverging one in the unitary limit arbitrarily
close to the Fermi energy.
