Imaginary geometry II: Reversibility of SLE.(.1;.2) for ..(0,4)

Given a simply connected planar domain D, distinct points x,y..D, and .>0, the Schramm.Loewner evolution SLE. is a random continuous non-self-crossing path in .....D from x to y. The SLE.(.1;.2) processes, defined for .1,.2>.2, are in some sense the most natural generalizations of SLE. . When ..4 , we prove that the law of the time-reversal of an SLE.(.1;.2) from x to y is, up to parameterization, an SLE.(.2;.1) from y to x. This assumes that the .force points. used to define SLE.(.1;.2) are immediately to the left and right of the SLE seed. A generalization to arbitrary (and arbitrarily many) force points applies whenever the path does not (or is conditioned not to) hit .D.{x,y} . The proof of time-reversal symmetry makes use of the interpretation of SLE.(.1;.2) as a ray of a random geometry associated to the Gaussian-free field. Within this framework, the time-reversal result allows us to couple two instances of the Gaussian-free field (with different boundary conditions) so that their difference is almost surely constant on either side of the path. In a fairly general sense, adding appropriate constants to the two sides of a ray reverses its orientation.