for A being Universal_Algebra
for B being Subset of A
for n being Nat
for x being set holds
( x in B |^ (n + 1) iff ( x in B or ex o being Element of dom the charact of A ex p being Element of the carrier of A * st
( x = (Den (o,A)) . p & p in dom (Den (o,A)) & rng p c= B |^ n ) ) )