for RFin being FinSequence of REAL st len RFin >= 1 holds
ex f being Real_Sequence st
( f . 1 = RFin . 1 & ( for n being Nat st 0 <> n & n < len RFin holds
f . (n + 1) = (f . n) + (RFin . (n + 1)) ) & Sum RFin = f . (len RFin) )