theorem Th5:
  -1 <= ind Af
proof
  Af in (Seq_of_ind T).(1+ind Af) by Def5;
  then
A1: (ind Af)+1 in dom(Seq_of_ind T) by FUNCT_1:def 2;
  0=-1+1;
  hence thesis by A1,XREAL_1:6;
end;
