YES

1 decompositions
 #0 -----------
   1: f(a'(),x) -> f(x,x)
   2: f(x,a'()) -> f(x,x)
   3: f(a'(),a'()) -> b()
   4: b() -> f(a'(),a'())

@Development Closedness
--- R
   1: f(a'(),x) -> f(x,x)
   2: f(x,a'()) -> f(x,x)
   3: f(a'(),a'()) -> b()
   4: b() -> f(a'(),a'())

--- S
   1: f(a'(),x) -> f(x,x)
   2: f(x,a'()) -> f(x,x)
   3: f(a'(),a'()) -> b()
   4: b() -> f(a'(),a'())