Using @anticommuting_fermion_group c d, you get a group of mutually anticommuting fermionic operators, e.g., to treat itinerant and localized electrons with different operators. Note that two different fermionic operators defined with independent @fermion_ops calls are assumed to refer to different (quasi-)particle species, and thus commute.

Example usage:

julia> using QuantumAlgebra; QuantumAlgebra.auto_normal_form()
julia> @anticommuting_fermion_group c d
julia> comm(cdag(),d())
2 c†() d()

julia> d(:i)*c(:k)
-c(k) d(i)

The operators within a group are ordered by definition order, not alphabetically as normally:

julia> @anticommuting_fermion_group y x
julia> x()*y()
-y() x()

For comparison, for different @fermion_ops:

julia> @fermion_ops g;
julia> @fermion_ops h;
julia> comm(gdag(),h())
0

julia> h()*g()
g() h()

Closes #9.