Indoles, VIII: Formation of Indolo[3,2‐b]carbazoles from 4,9‐Dihydro‐pyrano[3,4‐b] indol‐1(3H)‐ones Indole, 8.Mitt: Indolo[3,2‐b]carbazole aus 4,9‐Dihydropyrano[3,4‐b]indol‐1(3H)‐onen