Semigroups of semi-copulas and evolution of dependence at increase of age

Abstract

We consider a pair of exchangeable lifetimes X; Y and the families of the conditional survival functions F t(x;y) of (X t; Y t) given (X > t; Y > t).We analyze some properties of dependence and of ageing for F t(x;y) andsome relations among them ) of ( X t; Y t ) given ( X > t; Y > t ). We analyze some properties of dependence and of ageing for F t ( x; y ) and some relations among them.