* Michael Pozhidaev <m...@altlinux.ru> [Jan 14. 2014 14:08]:
> Hi all!
> 
> I'd like to better understand some zypp (maybe libsolv) implementation
> details. Could anybody help me, please!
> 
> The question is as follows: consider we have a couple of packages a and
> b. Dependencies rules imply that a requires b. Reflecting that clause
> should be as (not a or b), right?

Yes.
See http://en.opensuse.org/openSUSE:Libzypp_satsolver_basics on how to
translate package dependencies to SAT rules.

> 
> But if a is not chosen for installation b gets freedom to have any
> value, either true or false without any consequent breaks of a solution.

Correct. If a is not installed, it doesn't matter if b is installed or
not. However, if a is installed (not a => false), then b must be
installed to give a 'true' result of the equation.

> 
> What strategy do zypp use to left the b variable unchanged? I mean left
> corresponding package uninstalled if it was uninstalled. Is it possible
> to do that strictly or it always implies some probability?
> 

Equations are solved left-to-right. So if a is not installed, then
'not a' already is true and the 'or' part of the equation does not
need to be considered.


Hth,

Klaus
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