YES

   1: or(true(),true()) -> true()
   2: or(x2,x1) -> or(x1,x2)

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

--- S
   1: or(true(),true()) -> true()
   2: or(x2,x1) -> or(x1,x2)