Definition: Def. 11.02: Surface of a Solid Figure
The extremity of a solid (is) a surface.
Modern Formulation
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Mentioned in:
Definitions: 1
Proofs: 2 3 4
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References
Adapted from (subject to copyright, with kind permission)
 Fitzpatrick, Richard: Euclid's "Elements of Geometry"
Adapted from CC BYSA 3.0 Sources:
 Prime.mover and others: "Pr∞fWiki", https://proofwiki.org/wiki/Main_Page, 2016