The system of mirrors which will deviate a ray by an angle D while rotating an image an angle R is such that the dihedral angle A between the two mirrors is in accord with cosA = ±cosD/2 cosR/2. The position of the common edge bears a fixed but simple relationship to the initial and terminal ray. The system of two mirrors with fixed dihedral angle may be rotated about the common edge of the two mirrors as an axis to provide, within limits, a continuous multiplicity of solutions. Design techniques are included.
BERNARD S. LEE, "Oblique Reflecting Systems," J. Opt. Soc. Am. 39, 487-488 (1949)