reserve r,r1,g for Real,
  n,m,k for Nat,
  seq,seq1, seq2 for Real_Sequence,
  f,f1,f2 for PartFunc of REAL,REAL,
  x for set;
reserve r,r1,r2,g,g1,g2 for Real;

theorem
  (seq is divergent_to+infty implies -seq is divergent_to-infty) & (seq
  is divergent_to-infty implies -seq is divergent_to+infty)
by Th13,Th14;
