reserve x, x1, x2, y, y1, y2, z, z1, z2 for object, X, X1, X2 for set;
reserve E for non empty set;
reserve e for Element of E;
reserve u, u9, u1, u2, v, v1, v2, w, w1, w2 for Element of E^omega;
reserve F, F1, F2 for Subset of E^omega;
reserve i, k, l, n for Nat;
reserve TS for non empty transition-system over F;
reserve s, s9, s1, s2, t, t1, t2 for Element of TS;
reserve S for Subset of TS;

theorem
  ==>.-relation(TS) reduces [x, w], [y, v^w] implies v = <%>E
proof
  assume ==>.-relation(TS) reduces [x, w], [y, v^w];
  then len w >= len(v^w) by Th75;
  then len v + len w <= 0 + len w by AFINSQ_1:17;
  hence thesis by XREAL_1:6;
end;
