Commentary on Proposition XI.13

Back to Proposition XI.13.

[Folio 0299 | p. 295]

Simson added words to this as follows:

“Also, from a point above a plane there can be but one perpendicular to that plane; for, if there could be two, they would be parallel to one another [XI. 6], which is absurd.”

Euclid does not give this result, but we have already had it in the note above to XI. 4 (ad fin.).