reserve n,n1,n2,m for Nat,
  r,r1,r2,p,g1,g2,g for Real,
  seq,seq9,seq1 for Real_Sequence,
  y for set;

theorem Th11:
  seq is convergent & seq9 is convergent implies seq - seq9 is convergent
proof
  assume that
A1: seq is convergent and
A2: seq9 is convergent;
  -seq9 is convergent by A2;
  hence thesis by A1;
end;
