fact: Definition fcard_sigma {X} (Y : X -> Type) `{Finite X} `{forall x, Finite (Y x)} : fcard { x:X & Y x } = finadd (fun x => fcard (Y x)).
imports: Basics Types HSet Spaces.Nat.Core HFiber Factorization Truncations Colimits.Quotient Projective Fin