Definition: Def. 11.07: Similarly Inclined Planes
A plane is said to have been similarly inclined to a plane, as another to another, when the aforementioned angles of inclination are equal to one another.
Modern Formulation
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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