theorem Th81:
  for TS1 being non empty transition-system over F1, TS2 being non
  empty transition-system over F2 st the carrier of TS1 = the carrier of TS2 &
the Tran of TS1 = the Tran of TS2 holds x1, x2 ==>* y1, y2, TS1 implies x1, x2
  ==>* y1, y2, TS2
by Th34;
