 Tymoczko's "Generalizing Musical Intervals" contains one of the few extended critiques of transformational theory, arguing (1) that intervals are sometimes "local" objects that, like vectors, cannot be transported around a musical space; (2) that musical spaces often have boundaries, or multiple paths between the same points, both prohibited by Lewin's formalism; and (3) that transformational theory implicitly relies on notions of distance extraneous to the formalism as such.Although transformation theory is more than thirty years old, it did not become a widespread theoretical or analytical pursuit until the late 1990s.Following Lewin's revival (in GMIT) of Hugo Riemann's three contextual inversion operations on triads (parallel, relative, and Leittonwechsel) as formal transformations, the branch of transformation theory called Neo-Riemannian theory was popularized by Brian Hyer (1995), Michael Kevin Mooney (1996), Richard Cohn (1997), and an entire issue of the "Journal of Music Theory" (42/2, 1998).