Basterfield showed that if $X \in L \log L$ and $\{\mathscr{F}_n\}$ form a sequence of independent $\sigma$-fields, then $E(X\mid\mathscr{F}_n)\rightarrow EX$ a.s. His proof uses the theory of Orlicz spaces. We generalize Basterfield's theorem to the case of Markov-dependent $\sigma$-fields and also weaken the restrictions on $X$. Our approach is different from Basterfield's in that it is martingale-theoretic.
@article{1176994905,
author = {Isaac, Richard},
title = {Markov-Dependent $\sigma$-Fields and Conditional Expectations},
journal = {Ann. Probab.},
volume = {7},
number = {6},
year = {1979},
pages = { 1088-1091},
language = {en},
url = {http://dml.mathdoc.fr/item/1176994905}
}
Isaac, Richard. Markov-Dependent $\sigma$-Fields and Conditional Expectations. Ann. Probab., Tome 7 (1979) no. 6, pp. 1088-1091. http://gdmltest.u-ga.fr/item/1176994905/