for x, z1, z2 being object
for E being non empty set
for u, v being Element of E ^omega
for F being Subset of (E ^omega)
for TS being deterministic transition-system over F st u <> v & x,u -->. z1,TS & x,v -->. z2,TS holds
for w being Element of E ^omega holds
( not u ^ w = v & not v ^ w = u )