let X be set ; :: thesis: for L being List of X
for O being Operation of X
for n being Nat holds L WHEREle (O,n) = L WHERElt (O,(n + 1))

let L be List of X; :: thesis: for O being Operation of X
for n being Nat holds L WHEREle (O,n) = L WHERElt (O,(n + 1))

let O be Operation of X; :: thesis: for n being Nat holds L WHEREle (O,n) = L WHERElt (O,(n + 1))
let n be Nat; :: thesis: L WHEREle (O,n) = L WHERElt (O,(n + 1))
thus L WHEREle (O,n) c= L WHERElt (O,(n + 1)) :: according to XBOOLE_0:def 10 :: thesis: L WHERElt (O,(n + 1)) c= L WHEREle (O,n)
proof
let z be object ; :: according to TARSKI:def 3 :: thesis: ( not z in L WHEREle (O,n) or z in L WHERElt (O,(n + 1)) )
assume z in L WHEREle (O,n) ; :: thesis: z in L WHERElt (O,(n + 1))
then consider x being Element of X such that
A1: ( z = x & card (x . O) c= n & x in L ) ;
Segm (n + 1) = succ (Segm n) by NAT_1:38;
then card (x . O) in n + 1 by ;
hence z in L WHERElt (O,(n + 1)) by A1; :: thesis: verum
end;
let z be object ; :: according to TARSKI:def 3 :: thesis: ( not z in L WHERElt (O,(n + 1)) or z in L WHEREle (O,n) )
assume z in L WHERElt (O,(n + 1)) ; :: thesis: z in L WHEREle (O,n)
then consider x being Element of X such that
A2: ( z = x & card (x . O) in n + 1 & x in L ) ;
Segm (n + 1) = succ (Segm n) by NAT_1:38;
then card (x . O) c= n by ;
hence z in L WHEREle (O,n) by A2; :: thesis: verum