A Note on Irregularity of Two Dimensional Simple Hyperbolic Singularities

Deformation theory is an important aspect of the study about isolated singularities. The invariant called irregularity is very useful in the study on the deformation of isolated singu larities. In this note we give an optimal upper bound for a class of surface singularities by the computation of cohomology. Moreover a sufficient condition is given for the positivity of irreg ularity of some simple hyperbolic surface singularities. Therefore a class of surface singularities with non-rigid deformation is constructed.