On the Associativity of Gluing
  This paper studies the associativity of gluing of trajectories in Morse theory. We show that the associativity of gluing follows from of the existence of compatible manifold with face structures on the compactified moduli spaces. Using our previous work, we obtain the associativity of gluing in certain cases.   In particular, associativity holds when the ambient manifold is compact and the vector field is Morse-Smale. 
Lizhen Qin
math.GT math.SG