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