  The Lorentz transformation group $SO(m,n)$ is a group of Lorentz
transformations of order $(m,n)$, that is, a group of special linear
transformations in a pseudo-Euclidean space of signature $(m,n)$ that leave the
pseudo-Euclidean inner product invariant. A parametrization of $SO(m,n)$ is
presented, giving rise to the composition law of Lorentz transformations of
order $(m,n)$ in terms of parameter composition. The parameter composition, in
turn, gives rise to a novel group-like structure called a bi-gyrogroup.
Bi-gyrogroups form a natural generalization of gyrogroups where the latter form
a natural generalization of groups. Like the abstract gyrogroup, the abstract
bi-gyrogroup can play a universal computational role which extends far beyond
the domain of pseudo-Euclidean spaces.
