A set of lecture notes affectionately known as “Joe’s Little Book of [these systems]” is a companion to Polchinski’s textbook on these systems. Considering all surfaces of genus one under the Polyakov path integral constitutes the one-level analysis of these systems, whose simplest invariant model is the Nambu–Goto action. These systems trace out worldsheets (15[1])in spacetime, (15[1])and their boundary conditions create D-branes. Ed (15[1])(*) Witten combined several related theories of these (10[1])systems with supergravity into the 11-dimensional M-theory, providing a unification of quantum mechanics with general relativity. Particles are envisioned as vibrational modes of these systems in those namesake theories. For 10 points, name these one-dimensional systems that form the basis of an unverifiable theory of everything. ■END■