YES

   1: +(+(x1,x2),x3) -> +(x1,+(x2,x3))
   2: +(x1,x2) -> +(x2,x1)

@Jouannaud and Kirchner's criterion
--- R
   1: +(+(x1,x2),x3) -> +(x1,+(x2,x3))
   2: +(x1,x2) -> +(x2,x1)

--- S
   1: +(+(x1,x2),x3) -> +(x1,+(x2,x3))
   2: +(x1,x2) -> +(x2,x1)