Alexander E. Andreev, Andrea E.F. Clementi, Jose D.P. Rolim, and Luca
Weak Random Sources, Hitting Sets, and BPP Simulations.
ECCC TR 97-11.
Submitted, April 1997.
Departing significantly from previous related works, we do not use extractors; instead, we use OR-dispersers in combination with a tricky use of hitting sets borrowed from a paper of Andreev et al. (1996).
Of independent interest is our new (simplified) proof of the main result of Andreev et al. (1996). Our proof also yields some new hardness/randomness trade-offs for parallel classes.