for x1, x2, y1, y2, z1, z2 being object
for E being non empty set
for F being Subset of (E ^omega)
for TS being deterministic transition-system over F st x1,x2 ==>. y1,z1,TS & x1,x2 ==>. y2,z2,TS holds
( y1 = y2 & z1 = z2 )