YES

   1: or(T(),x1) -> T()
   2: or(x1,F()) -> x1
   3: or(or(x1,x2),x3) -> or(x1,or(x2,x3))
   4: or(x1,x2) -> or(x2,x1)

@Jouannaud and Kirchner's criterion
--- R
   1: or(T(),x1) -> T()
   2: or(x1,F()) -> x1
   3: or(or(x1,x2),x3) -> or(x1,or(x2,x3))
   4: or(x1,x2) -> or(x2,x1)

--- S
   1: or(T(),x1) -> T()
   2: or(x1,F()) -> x1
   3: or(or(x1,x2),x3) -> or(x1,or(x2,x3))
   4: or(x1,x2) -> or(x2,x1)