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

theorem Th6:
  for D being non empty set for f being non empty one-to-one
  FinSequence of D holds f/.len f..f = len f
proof
  let D be non empty set;
  let f be non empty one-to-one FinSequence of D;
A1: len f in dom f by FINSEQ_5:6;
A2: for i being Nat st 1 <= i & i < len f holds f.i <> f.len f
  proof
    let i be Nat such that
A3: 1 <= i and
A4: i < len f;
    i in dom f by A3,A4,FINSEQ_3:25;
    hence thesis by A1,A4,FUNCT_1:def 4;
  end;
  f/.len f = f.len f by A1,PARTFUN1:def 6;
  hence thesis by A1,A2,FINSEQ_6:2;
end;
