theorem Th103: :: REWRITE3:103

for x being object
for X being set
for E being non empty set
for F being Subset of (E ^omega)
for TS being non empty transition-system over F
for s being Element of TS holds
( s in x -succ_of (X,TS) iff ex t being Element of TS st
( t in X & t,x ==>* s,TS ) )