That checks out, you think: Loop is an Escheresque musical by a gay Black man about a gay Black man writing a musical about a gay Black man writing about himself. As Usher, Jackson’s composer hero, sits on a subway explaining his own musical (also called A Strange Loop) to a stranger, he cites Douglas Hofstadter’s book about “loops” of identity-constructing self-reference. Of course there would be two - Jackson’s stunning show is recursive, redundant, reflective, reflexive. Jackson’s “Big Black and Queer-Ass American Broadway” show, he gives two explanations for the title. In the course of A Strange Loop, Michael R. Jaquel Spivey (center) stars in A Strange Loop, at the Lyceum Theatre.