  The constraint algebra is derived in the second order tetrad Hamiltonian
formalism of the bigravity. This is done by a straightforward calculation
without involving any insights, implicit functions, and Dirac brackets. The
tetrad approach is the only way to present the bigravity action as a linear
functional of lapses and shifts, and the Hassan-Rosen transform (characterized
as "a complicated redefinition of the shift variable" according to the authors)
appears here not as an ansatz but as fixing of a Lagrange multiplier. A
comparison of this approach with the other ones is provided.
