  In the present paper we find generators of the mixed commutator subgroups of
relative elementary groups and obtain unrelativised versions of commutator
formulas in the setting of Bak's unitary groups. It is a direct sequel of our
similar results were obtained for $GL(n,R)$ and for Chevalley groups over a
commutative ring with 1, respectively. Namely, let $(A,\Lambda)$ be any form
ring and $n\ge 3$. We consider Bak's hyperbolic unitary group
$GU(2n,A,\Lambda)$. Further, let $(I,\Gamma)$ be a form ideal of $(A,\Lambda)$.
One can associate with $(I,\Gamma)$ the corresponding elementary subgroup
$FU(2n,I,\Gamma)$ and the relative elementary subgroup $EU(2n,I,\Gamma)$ of
$GU(2n,A,\Lambda)$. Let $(J,\Delta)$ be another form ideal of $(A,\Lambda)$. In
the present paper we prove an unexpected result that the non-obvious type of
generators for $\big[EU(2n,I,\Gamma),EU(2n,J,\Delta)\big]$, as constructed in
our previous papers with Hazrat, are redundant and can be expressed as products
of the obvious generators, the elementary conjugates
$Z_{ij}(ab,c)=T_{ji}(c)T_{ij}(ab)T_{ji}(-c)$ and $Z_{ij}(ba,c)$, and the
elementary commutators $Y_{ij}(a,b)=[T_{ji}(a),T_{ij}(b)]$, where
$a\in(I,\Gamma)$, $b\in(J,\Delta)$, $c\in(A,\Lambda)$. It follows that
$\big[FU(2n,I,\Gamma),FU(2n,J,\Delta)\big]=
\big[EU(2n,I,\Gamma),EU(2n,J,\Delta)\big]$. In fact, we establish much more
precise generation results. In particular, even the elementary commutators
$Y_{ij}(a,b)$ should be taken for one long root position and one short root
position. Moreover, $Y_{ij}(a,b)$ are central modulo
$EU(2n,(I,\Gamma)\circ(J,\Delta))$ and behave as symbols. This allows us to
generalise and unify many previous results,including the multiple elementary
commutator formula, and dramatically simplify their proofs.
