YES

Problem:
 qsort(nil()) -> nil()
 qsort(.(x,y)) -> ++(qsort(lowers(x,y)),.(x,qsort(greaters(x,y))))
 lowers(x,nil()) -> nil()
 lowers(x,.(y,z)) -> if(<=(y,x),.(y,lowers(x,z)),lowers(x,z))
 greaters(x,nil()) -> nil()
 greaters(x,.(y,z)) -> if(<=(y,x),greaters(x,z),.(y,greaters(x,z)))

Proof:
 DP Processor:
  DPs:
   qsort#(.(x,y)) -> greaters#(x,y)
   qsort#(.(x,y)) -> qsort#(greaters(x,y))
   qsort#(.(x,y)) -> lowers#(x,y)
   qsort#(.(x,y)) -> qsort#(lowers(x,y))
   lowers#(x,.(y,z)) -> lowers#(x,z)
   greaters#(x,.(y,z)) -> greaters#(x,z)
  TRS:
   qsort(nil()) -> nil()
   qsort(.(x,y)) -> ++(qsort(lowers(x,y)),.(x,qsort(greaters(x,y))))
   lowers(x,nil()) -> nil()
   lowers(x,.(y,z)) -> if(<=(y,x),.(y,lowers(x,z)),lowers(x,z))
   greaters(x,nil()) -> nil()
   greaters(x,.(y,z)) -> if(<=(y,x),greaters(x,z),.(y,greaters(x,z)))
  Usable Rule Processor:
   DPs:
    qsort#(.(x,y)) -> greaters#(x,y)
    qsort#(.(x,y)) -> qsort#(greaters(x,y))
    qsort#(.(x,y)) -> lowers#(x,y)
    qsort#(.(x,y)) -> qsort#(lowers(x,y))
    lowers#(x,.(y,z)) -> lowers#(x,z)
    greaters#(x,.(y,z)) -> greaters#(x,z)
   TRS:
    greaters(x,nil()) -> nil()
    greaters(x,.(y,z)) -> if(<=(y,x),greaters(x,z),.(y,greaters(x,z)))
    lowers(x,nil()) -> nil()
    lowers(x,.(y,z)) -> if(<=(y,x),.(y,lowers(x,z)),lowers(x,z))
   KBO Processor:
    argument filtering:
     pi(nil) = []
     pi(.) = [0,1]
     pi(lowers) = [0,1]
     pi(greaters) = []
     pi(<=) = []
     pi(if) = []
     pi(qsort#) = 0
     pi(greaters#) = 1
     pi(lowers#) = 1
    usable rules:
     greaters(x,nil()) -> nil()
     greaters(x,.(y,z)) -> if(<=(y,x),greaters(x,z),.(y,greaters(x,z)))
     lowers(x,nil()) -> nil()
     lowers(x,.(y,z)) -> if(<=(y,x),.(y,lowers(x,z)),lowers(x,z))
    weight function:
     w0 = 1
     w(lowers#) = w(greaters#) = w(qsort#) = w(if) = w(<=) = w(greaters) = w(
     lowers) = w(.) = w(nil) = 1
    precedence:
     greaters# ~ qsort# ~ <= ~ greaters ~ . > lowers# ~ if ~ lowers ~ nil
    problem:
     DPs:
      
     TRS:
      greaters(x,nil()) -> nil()
      greaters(x,.(y,z)) -> if(<=(y,x),greaters(x,z),.(y,greaters(x,z)))
      lowers(x,nil()) -> nil()
      lowers(x,.(y,z)) -> if(<=(y,x),.(y,lowers(x,z)),lowers(x,z))
    Qed