<math> <apply><forall/> <bvar><ci>a</ci></bvar> <bvar><ci>b</ci></bvar> <condition> <apply><and/> <apply><in/><ci>a</ci><reals/></apply> <apply><in/><ci>b</ci><reals/></apply> </apply> </condition> <apply><eq/> <apply><plus/><ci>a</ci><ci>b</ci></apply> <apply><plus/><ci>b</ci><ci>a</ci></apply> </apply> </apply> </math>