reserve P for Subset of TOP-REAL 2,
  f,f1,f2,g for FinSequence of TOP-REAL 2,
  p,p1,p2,q,q1,q2 for Point of TOP-REAL 2,
  r1,r2,r19,r29 for Real,
  i,j,k,n for Nat;

theorem Th5:
  for i, n being Nat holds 1 <= i & i+1 <= len f - n implies LSeg(f
  /^n,i) = LSeg(f,n+i)
proof
  let i, n be Nat;
  assume
A1: 1 <= i;
A2: n <= i+1+n by NAT_1:11;
  assume i+1 <= len f - n;
  then i+1+n <= len f by XREAL_1:19;
  then n <= len f by A2,XXREAL_0:2;
  hence thesis by A1,Th4;
end;
