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# Default Solver Policy
A solver policy defines behaviour variables of the dependency solver. It decides
which versions are considered newer than others, which packages should be
prefered over others and whether operations like downgrades or uninstall are
allowed.
## Selection of prefered Packages
The following describe package pool situations with user requests and the
resulting order in which the solver will try to install them.
The rules are to be applied in the order of these descriptions.
### Package versions
Packages: Av1, Av2, Av3
* Installed: Av2
Request: install A
* (Av3)
### Repository priorities
Packages Repo1.Av1, Repo2.Av1
* priority(Repo1) >= priority(Repo2) => (Repo1.Av1, Repo2.Av1)
* priority(Repo2) < priority(Repo2) => (Repo2.Av1, Repo1.Av1)
### Virtual Packages (provides)
Packages Av1, Bv1
* Av1 provides Xv1
* Bv1 provides Xv1
Request: install X
* priority(Av1.repo) >= priority(Bv1.repo) => (Av1, Bv1)
* priority(Av1.repo) < priority(Bv1.repo) => (Bv1, Av1)
### Package replacements
Packages: Av1, Bv2
* Bv2 replaces Av1
Request: install A
* priority(Av1.repo) > priority(Bv2.repo) => (Av1, Bv2)
* priority(Av1.repo) = priority(Bv2.repo) => (Av1, Bv2)
* priority(Av1.repo) < priority(Bv2.repo) => (Bv2, Av1)
Bv2.version is ignored, only the replacement version for A matters.