type I string theory
theory of strings where left- and right-movers are identified via orientifolding, obtained as IIB string theory with 32 spacetime-filling D9-branes (producing a O(32) gauge group) and a spacetime-filling O9-plane
theory of strings where left- and right-movers are identified via orientifolding, obtained as IIB string theory with 32 spacetime-filling D9-branes (producing a O(32) gauge group) and a spacetime-filling O9-plane