Here is a scan of the page from my Greek New Testament.

This highlights three words in verse 12.  Two of those words I didn't recognize...but the first (I discover when I research it a bit) only occurs 17 times in the NT, and the second only 4 times.  So I will never bother to memorize these.  I am happy to use my reader's edition NT, or to go to www.StepBible.orgg.

I recognized εἶναι as the present active infinitive form of ἐιμί, "to be".  I am a little surprised that my Greek NT included it at the bottom of the page, as it is an enormously common word.

On the other hand, ἐιμί is VERY irregular.  You need to memorize each form of it individually.  So from that point of view, it is a perfect candidate for the footnotes in this GNT edition.