YES

   1: F(x2,x1) -> c(x1)
   2: G(x2) -> x2
   3: f(x2) -> g(x2)
   4: g(x2) -> c(x2)

@Jouannaud and Kirchner's criterion
--- R
   1: F(x2,x1) -> c(x1)
   2: G(x2) -> x2
   3: f(x2) -> g(x2)
   4: g(x2) -> c(x2)

--- S
   1: F(x2,x1) -> c(x1)
   2: G(x2) -> x2
   3: f(x2) -> g(x2)
   4: g(x2) -> c(x2)