theorem Th8:
  seq is nonnegative implies not seq is convergent_to_-infty
proof
  assume
A1: seq is nonnegative;
  assume seq is convergent_to_-infty;
  then consider n be Nat such that
A2: for m be Nat st n<=m holds seq.m <= -1;
  seq.n <= -1 by A2;
  hence contradiction by A1,SUPINF_2:51;
end;
