Complex boolean sentence as a tree

[Thomas de Grenier de Latour]

Hi, 

I'm looking for a package that would help me to write complex boolean
sentences, like "the cat is black or it is white and it eats mice" (it's
for a very technical paper about cats ;) without ambiguite. I think
about something like this:

and
 |- or
 |  |- the cat is black
 |  |- it is white
 |- it eats mice

See the difference with this, which would be a bad interpretation of my
cat definition:

or
 |- the cat is black
 |- and
     |- it is white
     |- it eats mice

I manage to do something similar using the itemize environment, but it
is less clear:

and
- or 
  - 
  - it is white
- it eat mice

I've found packages to draw trees on the CTAN, but only things like this
which takes more place and is less readable:

       and
      /   \
     or  it eat mice
    /  \
   /   it is white
  / 
 the cat is black 



Any idea ? 
Thanks for your help.

Thomas.