Plato, Meno 85a

τέμνουσα δίχα ἕκαστον τούτων τῶν χωρίων; ναί. οὐκοῦν τέτταρες αὗται γίγνονται γραμμαὶ ἴσαι, περιέχουσαι τουτὶ τὸ χωρίον; γίγνονται γάρ. σκόπει δή· πηλίκον τί ἐστιν τοῦτο τὸ χωρίον; οὐ μανθάνω. οὐχὶ τεττάρων ὄντων τούτων ἥμισυ ἑκάστου ἑκάστη ἡ γραμμὴ ἀποτέτμηκεν ἐντός; ἢ οὔ; ναί. πόσα οὖν τηλικαῦτα ἐν τούτῳ ἔνεστιν; τέτταρα. πόσα δὲ ἐν τῷδε; δύο. τὰ δὲ τέτταρα τοῖν δυοῖν τί ἐστιν; διπλάσια. τόδε οὖν

cut in two each of these spaces? Yes. And have we here four equal lines containing this space? We have. Now consider how large this space is. I do not understand. Has not each of the inside lines cut off half of each of these four spaces? Yes. And how many spaces of that size are there in this part? Four. And how many in this? Two. And four is how many times two? Twice.