fact: Definition inaccessibleU U x := [/\ cardinalU U x, ssub omega0 x, (forall a b, cardinalU U a -> cardinalU U b -> ssub a x -> ssub b x -> ssub (powerU U a b) x) & (forall a, cardinalU U a -> a <> emptyset -> ssub a x -> (powerU U x a) = x) ].
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)