Rubio de Francia's extrapolation theorem for $B_p$ weights.

In this paper, we prove some of Rubio de Francia's extrapolation results for the class $B_p$ of weights for which the Hardy operator is bounded on $L^p(w)$ restricted to decreasing functions. Applications to the boundedness of operators on $L^p_{{rm dec}}(w)$ are given. We also present an extension to the $B_infty $ case and some connections with classical $A_p$ theory. [ABSTRACT FROM AUTHOR]