theorem Th15: :: MODAL_1:20

for Z being Tree
for o being Element of Z st o <> Root Z holds
( Z | o, { (o ^ s9) where s9 is Element of NAT * : o ^ s9 in Z } are_equipotent & not Root Z in { (o ^ w9) where w9 is Element of NAT * : o ^ w9 in Z } )