  We discuss the fact that $k_t$-factorization calculations for heavy-quark
production include only the $gg\rightarrow Q\bar{Q}$ contribution. The cases of
fixed-flavor-number scheme and variable-flavor-number scheme calculations are
analyzed separately. For the latter, we show that, similarly to the collinear
factorization, the main contribution is given by the $Qg\rightarrow Qg$
process. In this scheme, calculations including only the $gg$ contribution
should show a large discrepancy with the data. We show that, if they do not, it
is because they include (effectively) a large $K$ factor.
