User blog comment:Nayuta Ito/Ita-Chihaya number/@comment-10429372-20140823084853

Shoudn't it be SH(N,a,0,M) = SH(N,a-1,SH(a-1,a,M),M) or even SH(N,a,0,M) = SH(N,a-1,SH(N,a-1,a,M),M)?

Beacause the current rules doesn't follow your example.