Five “Infeasibility” is a noun and “unfeasible”, as nan gray notes, is definitely an adjective herisson KeldericKelderic 47211 gold badge44 silver badges88 bronze badges ten You have to deliver proof. Long ago, considered one of my instructors advocated "none is", so I use that (other than occasionally I do not). https://dominickisckr.governor-wiki.com/1840335/5_easy_facts_about_5_45_bulk_ammo_described