
theorem
  for n being Nat st n>0 holds FTSL1 n is filled
proof
  let n be Nat;
  assume n>0;
  then
A1: FTSL1 n=RelStr(# Seg n,Nbdl1 n #) by Def4;
  let x be Element of FTSL1 n;
  x in Seg n by A1;
  then reconsider i=x as Element of NAT;
  U_FT x= {i,max(i-'1,1),min(i+1,n)} by A1,Def3;
  hence thesis by ENUMSET1:def 1;
end;
