reserve G for Go-board,
  i,j,k,m,n for Nat;

theorem Th7:
  for f,g being FinSequence holds len f <= len(f^'g)
proof
  let f,g be FinSequence;
  f ^' g = f^(2, len g)-cut g by FINSEQ_6:def 5;
  then len(f^'g) = len f + len(2, len g)-cut g by FINSEQ_1:22;
  hence thesis by NAT_1:11;
end;
