Right. Plato wasn’t on curriculum when I was in school. I suppose in the five undergrad courses I took in philosophy he was probably mentioned for a day or two in the Phil 101 (Will Durant, textbook).
On the other hand, Jesus (in John) makes it easy to detect an affirmation by using a formula: ἀμὴν ἀμὴν λέγω ὑμῖν
Not to imply that there are not ambiguities involved, there are.
John 1:51 καὶ λέγει αὐτῷ· ἀμὴν ἀμὴν λέγω ὑμῖν, ὄψεσθε τὸν οὐρανὸν ἀνεῳγότα καὶ τοὺς ἀγγέλους τοῦ θεοῦ ἀναβαίνοντας καὶ καταβαίνοντας ἐπὶ τὸν υἱὸν τοῦ ἀνθρώπου.
John 3:3 ἀπεκρίθη Ἰησοῦς καὶ εἶπεν αὐτῷ· ἀμὴν ἀμὴν λέγω σοι, ἐὰν μή τις γεννηθῇ ἄνωθεν, οὐ δύναται ἰδεῖν τὴν βασιλείαν τοῦ θεοῦ.
John 3:5 ἀπεκρίθη Ἰησοῦς· ἀμὴν ἀμὴν λέγω σοι, ἐὰν μή τις γεννηθῇ ἐξ ὕδατος καὶ πνεύματος, οὐ δύναται εἰσελθεῖν εἰς τὴν βασιλείαν τοῦ θεοῦ.
John 3:11 ἀμὴν ἀμὴν λέγω σοι ὅτι ὃ οἴδαμεν λαλοῦμεν καὶ ὃ ἑωράκαμεν μαρτυροῦμεν, καὶ τὴν μαρτυρίαν ἡμῶν οὐ λαμβάνετε.
John 5:19 Ἀπεκρίνατο οὖν ὁ Ἰησοῦς καὶ ἔλεγεν αὐτοῖς· ἀμὴν ἀμὴν λέγω ὑμῖν, οὐ δύναται ὁ υἱὸς ποιεῖν ἀφ᾿ ἑαυτοῦ οὐδὲν ἐὰν μή τι βλέπῃ τὸν πατέρα ποιοῦντα· ἃ γὰρ ἂν ἐκεῖνος ποιῇ, ταῦτα καὶ ὁ υἱὸς ὁμοίως ποιεῖ.
John 5:24 Ἀμὴν ἀμὴν λέγω ὑμῖν ὅτι ὁ τὸν λόγον μου ἀκούων καὶ πιστεύων τῷ πέμψαντί με ἔχει ζωὴν αἰώνιον καὶ εἰς κρίσιν οὐκ ἔρχεται, ἀλλὰ μεταβέβηκεν ἐκ τοῦ θανάτου εἰς τὴν ζωήν. 25 ἀμὴν ἀμὴν λέγω ὑμῖν ὅτι ἔρχεται ὥρα καὶ νῦν ἐστιν ὅτε οἱ νεκροὶ ἀκούσουσιν τῆς φωνῆς τοῦ υἱοῦ τοῦ θεοῦ καὶ οἱ ἀκούσαντες ζήσουσιν.
John 6:26 Ἀπεκρίθη αὐτοῖς ὁ Ἰησοῦς καὶ εἶπεν· ἀμὴν ἀμὴν λέγω ὑμῖν, ζητεῖτέ με οὐχ ὅτι εἴδετε σημεῖα, ἀλλ᾿ ὅτι ἐφάγετε ἐκ τῶν ἄρτων καὶ ἐχορτάσθητε.
John 6:32 εἶπεν οὖν αὐτοῖς ὁ Ἰησοῦς· ἀμὴν ἀμὴν λέγω ὑμῖν, οὐ Μωϋσῆς δέδωκεν ὑμῖν τὸν ἄρτον ἐκ τοῦ οὐρανοῦ, ἀλλ᾿ ὁ πατήρ μου δίδωσιν ὑμῖν τὸν ἄρτον ἐκ τοῦ οὐρανοῦ τὸν ἀληθινόν·
John 6:47 ἀμὴν ἀμὴν λέγω ὑμῖν, ὁ πιστεύων ἔχει ζωὴν αἰώνιον.
John 6:53 εἶπεν οὖν αὐτοῖς ὁ Ἰησοῦς· ἀμὴν ἀμὴν λέγω ὑμῖν, ἐὰν μὴ φάγητε τὴν σάρκα τοῦ υἱοῦ τοῦ ἀνθρώπου καὶ πίητε αὐτοῦ τὸ αἷμα, οὐκ ἔχετε ζωὴν ἐν ἑαυτοῖς.
John 8:34 ἀπεκρίθη αὐτοῖς ὁ Ἰησοῦς· ἀμὴν ἀμὴν λέγω ὑμῖν ὅτι πᾶς ὁ ποιῶν τὴν ἁμαρτίαν δοῦλός ἐστιν τῆς ἁμαρτίας.
John 8:51 ἀμὴν ἀμὴν λέγω ὑμῖν, ἐάν τις τὸν ἐμὸν λόγον τηρήσῃ, θάνατον οὐ μὴ θεωρήσῃ εἰς τὸν αἰῶνα.
John 8:58 εἶπεν αὐτοῖς Ἰησοῦς· ἀμὴν ἀμὴν λέγω ὑμῖν, πρὶν Ἀβραὰμ γενέσθαι ἐγὼ εἰμί.
John 10:1 Ἀμὴν ἀμὴν λέγω ὑμῖν, ὁ μὴ εἰσερχόμενος διὰ τῆς θύρας εἰς τὴν αὐλὴν τῶν προβάτων ἀλλὰ ἀναβαίνων ἀλλαχόθεν ἐκεῖνος κλέπτης ἐστὶν καὶ λῃστής·
John 10:7 Εἶπεν οὖν πάλιν ὁ Ἰησοῦς· ἀμὴν ἀμὴν λέγω ὑμῖν ὅτι ἐγώ εἰμι ἡ θύρα τῶν προβάτων.
John 12:24 ἀμὴν ἀμὴν λέγω ὑμῖν, ἐὰν μὴ ὁ κόκκος τοῦ σίτου πεσὼν εἰς τὴν γῆν ἀποθάνῃ, αὐτὸς μόνος μένει· ἐὰν δὲ ἀποθάνῃ, πολὺν καρπὸν φέρει.
John 13:16 ἀμὴν ἀμὴν λέγω ὑμῖν, οὐκ ἔστιν δοῦλος μείζων τοῦ κυρίου αὐτοῦ οὐδὲ ἀπόστολος μείζων τοῦ πέμψαντος αὐτόν.
John 13:20 ἀμὴν ἀμὴν λέγω ὑμῖν, ὁ λαμβάνων ἄν τινα πέμψω ἐμὲ λαμβάνει, ὁ δὲ ἐμὲ λαμβάνων λαμβάνει τὸν πέμψαντά με. 21 Ταῦτα εἰπὼν [ὁ] Ἰησοῦς ἐταράχθη τῷ πνεύματι καὶ ἐμαρτύρησεν καὶ εἶπεν· ἀμὴν ἀμὴν λέγω ὑμῖν ὅτι εἷς ἐξ ὑμῶν παραδώσει με.
John 13:38 ἀποκρίνεται Ἰησοῦς· τὴν ψυχήν σου ὑπὲρ ἐμοῦ θήσεις; ἀμὴν ἀμὴν λέγω σοι, οὐ μὴ ἀλέκτωρ φωνήσῃ ἕως οὗ ἀρνήσῃ με τρίς.
John 14:12 Ἀμὴν ἀμὴν λέγω ὑμῖν, ὁ πιστεύων εἰς ἐμὲ τὰ ἔργα ἃ ἐγὼ ποιῶ κἀκεῖνος ποιήσει καὶ μείζονα τούτων ποιήσει, ὅτι ἐγὼ πρὸς τὸν πατέρα πορεύομαι·
John 16:20 ἀμὴν ἀμὴν λέγω ὑμῖν ὅτι κλαύσετε καὶ θρηνήσετε ὑμεῖς, ὁ δὲ κόσμος χαρήσεται· ὑμεῖς λυπηθήσεσθε, ἀλλ᾿ ἡ λύπη ὑμῶν εἰς χαρὰν γενήσεται.
John 16:23 Καὶ ἐν ἐκείνῃ τῇ ἡμέρᾳ ἐμὲ οὐκ ἐρωτήσετε οὐδέν. ἀμὴν ἀμὴν λέγω ὑμῖν, ἄν τι αἰτήσητε τὸν πατέρα ἐν τῷ ὀνόματί μου δώσει ὑμῖν.
John 21:18 ἀμὴν ἀμὴν λέγω σοι, ὅτε ἦς νεώτερος, ἐζώννυες σεαυτὸν καὶ περιεπάτεις ὅπου ἤθελες· ὅταν δὲ γηράσῃς, ἐκτενεῖς τὰς χεῖράς σου, καὶ ἄλλος σε ζώσει καὶ οἴσει ὅπου οὐ θέλεις.