YES
TRS:
 {  f(x) -> g(x),
  f(a()) -> f(b()),
  g(b()) -> g(a())}
 DP:
  Strict:
   {  f#(x) -> g#(x),
    f#(a()) -> f#(b()),
    g#(b()) -> g#(a())}
  Weak:
  {  f(x) -> g(x),
   f(a()) -> f(b()),
   g(b()) -> g(a())}
  EDG:
   {(f#(x) -> g#(x), g#(b()) -> g#(a()))
    (f#(a()) -> f#(b()), f#(x) -> g#(x))}
   SCCS:
    
    Qed