As Russia struggles toward a stable democracy against a reactionary communist backlash, here's a potent reminder of the bad old days. Inspired by the cases of dissidents Victor Fainberg and Vladimir Bukovsky, Tom Stoppard's intense, dazzlingly witty one-act concerns two prisoners--sorry, make that patients--in a Russian insane asylum. One is an outspoken foe of Soviet dictatorship; the other is a lunatic who hears music in his head. Taking his title from the music student's mnemonic phrase for the notes of the treble clef, Stoppard explores the political, psychological, and aesthetic implications of nonconformism in a totalitarian system, represented by a partly cynical, partly compassionate doctor whose job is to brainwash malcontents into "good boys" of the state. Packed with Stoppard's particular brand of ingenious puns and conundrums, EGBDF calls for an onstage orchestra to perform the madman's imagined music (composed by Andre Previn, who conceived the work) as tightly scored accompaniment to the drama. The cost involved means that this marvelous play is rarely performed unless it has stars to boost the box office--as it does in this touring production with Patrick Stewart, Jonathan Frakes, Brent Spiner, and Gates McFadden of the popular TV series Star Trek: The Next Generation. Frakes plays the hunger-striking dissident, Spiner his refined but insane cell mate; Stewart, who also directs, plays the doctor--the same role he portrayed in 1977, when EGBDF had its premiere under the auspices of the London Symphony Orchestra with Ian McKellen and John Wood in the leads. Chicago Theatre, 175 N. State, 902-1500. April 10 and 11: Saturday, 8 PM; Sunday, 2 PM. $30-$50.