for T, T1 being Tree
for P being AntiChain_of_Prefixes of T st P <> {} holds
tree (T,P,T1) = { t1 where t1 is Element of T : for p being FinSequence of NAT st p in P holds
not p is_a_prefix_of t1 } \/ { (p ^ s) where p is Element of T, s is Element of T1 : p in P }