theorem Th41:
  p = VFunc(f1,f2,f3).t iff p.1 = f1.t & p.2 = f2.t & p.3 = f3.t
proof
  thus p = VFunc(f1,f2,f3).t implies p.1 = f1.t & p.2 = f2.t & p.3 = f3.t
  proof
    assume p = VFunc(f1,f2,f3).t;
    then p = |[ f1.t,f2.t,f3.t ]| by Def5;
    hence thesis;
  end;
  assume p.1 = f1.t & p.2 = f2.t & p.3 = f3.t;
  then p = |[ f1.t,f2.t,f3.t ]| by Th1;
  hence p = VFunc(f1,f2,f3).t by Def5;
end;
