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