Structures of Banach function spaces that are derived from the theory of martingales

As a consequence of this research, we obtained a lot of theorems which show that we can analyze some structures of Banach function spaces by using martingale theory. For example we proved that, when X is a Banach function space, somenecessary and sufficient conditions which ensure that certain kinds of martingaleinequalities are valid in X can be expressed in terms of the rearrangement-invariance of X and the Boyd indices of X. This result shows that there are close connections between the validity of martingale inequalities and the structures of Banach function spaces.