theorem Th15:
  for f be FinSequence st len f >= 3 holds Center f < len f
proof
  let f be FinSequence;
  assume len f >= 3;
  then len f+(2+1) <= len f+len f by XREAL_1:6;
  then len f+2+1 <= 2*len f;
  then (len f+2+1+1) div 2 <= len f by NAT_2:25;
  then (len f+2+(1+1)) div 2 <= len f;
  then (len f+2) div 2+1 <= len f by NAT_2:14;
  then (len f+2) div 2 < len f by NAT_1:13;
  then len f div 2 + 1 < len f by NAT_2:14;
  hence thesis by JORDAN1A:def 1;
end;
