theorem Th55: :: CARD_FIN:56

for Fy being finite-yielding Function
for X being finite set st dom Fy = X holds
for XFS being XFinSequence of INT st dom XFS = card X & ( for n being Nat st n in dom XFS holds
XFS . n = ((- 1) |^ n) * (Card_Intersection (Fy,(n + 1))) ) holds
card (union (rng Fy)) = Sum XFS