I have a basic question about NET Bible footnote. The note for Matt 17:21 says:
Many important MSS (א* B Θ 0281 33 579 892 pc e ff1 sys,c sa) do not include 17:21 "But this kind does not go out except by prayer and fasting." The verse is included in א2 C D L W Ë1,13 Ï lat, but is almost certainly not original.
The א stands for Codex Sinaiticus right? But what is the difference between א* and א2?
I couldn't find an explanation of this online. Can you please explain this to me.