Strip away the subtext. Ignore the fact that the two characters in Suzan-Lori Parks’ gripping play Topdog/Underdog are called Lincoln and Booth, and brush aside the semiotic entanglements swelling up under names like that. Just consider this simple, hair-trigger premise: Jeffrey Wright, 36, and Don Cheadle, 37, two American actors magnetic and deft enough to make a subway schedule sound like Death of a Salesman, are playing brothers. Wright is the consummate older brother: blase, unruffled, masking a lethal germ of failure, sneaky enough to wield his seniority like a flyswatter when necessary. Cheadle is the consummate younger brother: a striver, a pupil, itchy for attention, both one step behind and one very crucial step ahead. This was the scene at Manhattan’s Public Theater as they climbed into Topdog/Underdog’s engine of fraternal love and combat. Credit the success to celluloid casting, okay, but it was more than that; here was chemistry of the most combustible strain. Each night Wright glanced out, shuffled a deck of cards for a game of three-card monte, and said: ”Watch me now.” Nobody had any choice.