  The power spectrum and bispectrum of dark matter tracers are key and
complementary probes of the Universe. Next-generation surveys will deliver good
measurements of the bispectrum, opening the door to improved cosmological
constraints and the breaking of parameter degeneracies, from the combination of
the power spectrum and bispectrum. Multi-tracer power spectra have been used to
suppress cosmic variance and mitigate the effects of nuisance parameters and
systematics. We present a bispectrum multi-tracer formalism that can be applied
to next-generation survey data. Then we perform a simple Fisher analysis to
illustrate qualitatively the improved precision on primordial non-Gaussianity
that is expected to come from the bispectrum multi-tracer. In addition, we
investigate the parametric dependence of conditional errors from multi-tracer
power spectra and multi-tracer bispectra, on the differences between the biases
and the number densities of two tracers. Our results suggest that optimal
constraints arise from maximising the ratio of number densities, the difference
between the linear biases, the difference between the quadratic biases, and the
difference between the products $b_1\,b_\Phi$ for each tracer, where $b_\Phi$
is the bias for the primordial potential.
