I n = A + ( A B + ( A B 2 + ( [?] A B q  @-@  1 + B q I n  @-@  p q [?] ) ) ) { \ displaystyle I _ { n } = A + \ left ( AB + \ left ( AB ^ { 2 } + \ left ( \ cdots AB ^ { q @-@ 1 } + B ^ { q } I _ { n @-@ pq } \ cdots \ right ) \ right ) \ right ) \ , \ ! }.
