n4→n1n_{4} \rightarrow n_{1}n4→n1
n4→n2\mathrm{n}_{4} \rightarrow \mathrm{n}_{2}n4→n2
n5→n2\mathrm{n}_{5} \rightarrow \mathrm{n}_{2}n5→n2
n6→n3\mathrm{n}_{6} \rightarrow \mathrm{n}_{3}n6→n3