  We demonstrate in detail how the space of two-dimensional quantum field
theories can be parametrized by off-shell closed string states. The dynamic
equation corresponding to the condition of conformal invariance includes an
infinite number of higher order terms, and we give an explicit procedure for
their calculation. The symmetries corresponding to equivalence relations of CFT
are described. In this framework we show how to perform nonperturbative
analysis in the low-energy limit and prove that it corresponds to the
Brans-Dicke theory of gravity interacting with a skew symmetric tensor field.
(Talk presented at the Gursey memorial conference, Istanbul, Turkey, June,
1994.)
