theorem Th1: :: HENMODEL:1

for n being Nat
for A being non empty finite Subset of NAT
for f being Function of n,A st ex m being Nat st succ m = n & rng f = A & ( for n, m being Nat st m in dom f & n in dom f & n < m holds
f . n in f . m ) holds
f . (union n) = union (rng f)