  In this paper, we classify EF topological orders for 3+1D bosonic systems
where some emergent pointlike excitations are fermions. (1) We argue that all
3+1D bosonic topological orders have gappable boundary. (2) All the pointlike
excitations in EF topological orders are described by the representations of
$G_f=Z_2^f\leftthreetimes_{e_2} G_b$ -- a $Z_2^f$ central extension of a finite
group $G_b$ characterized by $e_2\in H^2(G_b,Z_2)$. (3) We find that the EF
topological orders are classified by 2+1D anomalous topological orders
$\mathcal{A}_b^3$ on their unique canonical boundary. Here $\mathcal{A}_b^3$ is
a unitary fusion 2-category with simple objects labeled by $\hat
G_b=Z_2^m\leftthreetimes G_b$. $\mathcal{A}_b^3$ also has one invertible
fermionic 1-morphism for each object as well as quantum-dimension-$\sqrt 2$
1-morphisms that connect two objects $g$ and $gm$, where $g\in \hat G_b$ and
$m$ is the generator of $Z_2^m$. (4) When $\hat G_b$ is the trivial $Z_2^m$
extension, the EF topological orders are called EF1 topological orders, which
is classified by simple data $(G_b,e_2,n_3,\nu_4)$. (5) When $\hat G_b$ is a
non-trivial $Z_2^m$ extension, the EF topological orders are called EF2
topological orders, where some intersections of three stringlike excitations
must carry Majorana zero modes. (6) Every EF2 topological order with
$G_f=Z_2^f\leftthreetimes G_b$ can be associated with a EF1 topological order
with $G_f=Z_2^f\leftthreetimes \hat G_b$. (7) We find that all EF topological
orders correspond to gauged 3+1D fermionic symmetry protected topological (SPT)
orders with a finite unitary symmetry group. (8) We further propose that the
general classification of 3+1D topological orders with finite unitary
symmetries for bosonic and fermionic systems can be obtained by gauging or
partially gauging the finite symmetry group of 3+1D SPT phases of bosonic and
fermionic systems.
