Some minimal elements for a partial order of prime knots
  A partial order on the set of prime knots can be defined by the existence of an epimorphism between knot groups. We prove that all the prime knots with up to $6$ crossings are minimal. We also show that each fibered knot with the irreducible Alexander polynomial is minimal. 
Teruaki Kitano and Masaaki Suzuki
math.GT