YES

   1: p(x1) -> q(x1)
   2: p(x1) -> r(x1)
   3: q(x1) -> s(p(x1))
   4: r(x1) -> s(p(x1))
   5: s(x1) -> f(p(x1))

@Development Closedness
--- R
   1: p(x1) -> q(x1)
   2: p(x1) -> r(x1)
   3: q(x1) -> s(p(x1))
   4: r(x1) -> s(p(x1))
   5: s(x1) -> f(p(x1))

--- S
   1: p(x1) -> q(x1)
   2: p(x1) -> r(x1)
   3: q(x1) -> s(p(x1))
   4: r(x1) -> s(p(x1))
   5: s(x1) -> f(p(x1))