1. M.F. Atiyah, I.G. Macdonald, Introduction to commutative algebra, Addison-Wesley, Reading, Mass. 1969
2. A. Alzati, G. Ottaviani, A linear bound on the t-normality of codimension two subvarieties ofP n, Journal reine angew. Math409, 35–40 (1990)
3. J.M. Boardman, Singularities of differentiable maps, Publ. I.H.E.S.33, 21–57 (1967)
4. A. Grothendieck, J. Dieudonné, Elements de géométrie algébrique, Chap. IV. Publ. Math. IHES32 (1967)
5. Graduate Texts in Math;M. Golubitsky,1973