D.J. Gross, A.A. Migdal, "Nonperturbative two-dimensional quantum gravity," Physical Review Letters, 64:127-30, 1990.
D.J. Gross, A.A. Migdal, "Nonperturbative solution of the Ising model on a random surface," Physical Review Letters, 64:717-20, 1990.
D.J. Gross, N. Miljkovic, "A nonperturbative solution of D=1 string theory," Physics Letters B, 238:217-23, 1990.
David J. Gross (Joseph Henry Laboratories, Princeton University): "String theory, which contends to yield a unified theory of gravity and matter, is one of the most active and exciting areas of research in theoretical physics. A deep, conceptual framework for the theory, as well as nonperturbative control over it, is still lacking. One hopes to gain insight into these problems by exploring simple toy models of string theory that might be soluble. In the first of these papers Migdal and I (and, at the same time, M.R. Douglas and S.H. Shenker [Nuclear Physics B, 335:635-54, 1990] and E. BrEzin and V.A. Kazakov...