rillt[7], still[7], stils[6], irrst[5], sirrt[5], risst[5],
rill[6], till[6], list[5], stil[5], sirr[4], riss[4], sirs[4], irrt[4], rist[4], isst[4],
irr[3], sir[3], iss[3], ist[3],
si[2], ti[2], st[2],