NO

1 decompositions
 #0 -----------
   1: c() -> h(c(),c())
   2: f(c()) -> c()
   3: f(b()) -> b()
   4: a() -> b()
   5: a() -> h(h(a(),a()),h(c(),b()))

unjoinable peak
    f(h(c(),c()))
*<- f(c()) ->*
    h(c(),c())