Peter Petrov

Title:
Homological and homotopical variation operators

Abstract:
After reminding the classical Zariski and Zariski – van Kampen theorems, 
and Lefschtetz first and second theorems, some generalizations looking at 
their possible unification are formulated, and homological and homotopical 
variation operators are defined. They are a tool for some further results 
proposed by Chéniot and Libgober.  At the end is mentioned a conjecture 
of Chéniot – Eyral, which would unify the Zariski – van Kampen theorem 
and the second Lefschetz theorem.