gentoo problem



There seems to be a problem using Maxima on an AMD64.
I get the following message when using gentoo.
Any ideas?  (Also, who is creating the gentoo ebuilds?)

bash-2.05b# emerge -p maxima

These are the packages that I would merge, in order:

Calculating dependencies
!!! all ebuilds that could satisfy "maxima" have been masked.
!!! possible candidates are:
- app-sci/maxima-5.9.0 (masked by: missing keyword)
- app-sci/maxima-5.9.0-r1 (masked by: missing keyword)
- app-sci/maxima-5.9.0-r2 (masked by: missing keyword)

!!! Error calculating dependencies. Please correct.