Board Thread:Theories and Speculation/@comment-35685868-20180605140514

according to this wiki hiruzen "was renowned as The Professor (プロフェッサー, Purofessā) due to his mastery of all forms of shinobi combat, reputed for having advanced knowledge and/or skill of all the techniques to ever exist within Konoha, including the many Hiden techniques." so did he know the flying rajin if so why did he never use it 