Definition: Def. 11.08: Parallel Planes
(Definition 8 from Book 11 of Euclid's “Elements”)
Parallel planes are those (planes) which do not meet (one another).
Modern Formulation
Parallel planes are those which (extended infinitely) have no points in common.
Mentioned in:
Definitions: 1
Proofs: 2 3 4 5 6 7
Propositions: 8 9 10 11
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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