let v be Vertex of G; :: thesis: ( v is endvertex implies not v is cut-vertex )
assume A1: v is endvertex ; :: thesis: not v is cut-vertex
set H = the removeVertex of G,v;
G .numComponents() = the removeVertex of G,v .numComponents() by A1, Th45;
then not G .numComponents() in the removeVertex of G,v .numComponents() ;
hence not v is cut-vertex by GLIB_002:def 10; :: thesis: verum