Question: What word is both the name of Euphronius of the Athenian dem Sunium's son and is also one of Plato's diaglogues concerning the nature of knowledge?
Sentence (from "Theaetetus (mathematician)"): His principal contributions were on irrational lengths, which was included in "Book X" of Euclid's "Elements", and proving that there are precisely five regular convex polyhedra.
Relevant evidence: No