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Definitions for the National Library of Medicine's Permanence Levels

Permanence Not Guaranteed:
The National Library of Medicine has made no commitment to retain this resource. It could become unavailable at any time. Its identifier could be changed.

Permanent: Dynamic Content:
The National Library of Medicine has made a commitment to keep this resource permanently available. Its identifier will always provide access to the resource. Its content could be revised, replaced or recaptured.

Permanent: Stable Content:
The National Library of Medicine has made a commitment to keep this resource permanently available. Its identifier will always provide access to the resource. Its content is subject only to minor corrections or additions.

Permanent: Unchanging Content:
The National Library of Medicine has made a commitment to keep this resource permanently available. Its identifier will always provide access to the resource. Its content will not change.

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