YES

1 decompositions
 #1 -----------
   1: a() -> f(c())

@Knuth and Bendix' criterion
--- R
   1: a() -> f(c())

--- S
   1: a() -> f(c())


NOTE: input TRS is reduced

original is
   1: a() -> f(c())
   2: c() -> c()

reduced to
   1: a() -> f(c())