Degeneration, rigidity and irreducible components of Hopf algebras
  The aim of this work is to discuss the concepts of degeneration, deformation and rigidity, and to apply them to the geometric study of the varieties of Hopf algebras. The main result is the description of the n-dimensional rigid Hopf algebras and the irreducible components for n=p^2, p prime and for n<14. 
Abdenacer Makhlouf