Why in the Rambam when he speaks of what will happen when Mosiach comes there is no mention of Eliyahu Hanavi when in the gemara [Eiruvin 43b] it says that Eliyahu will come first like it says in the Navi[Malachi 3:23} "Behold I send unto you Eliyahu the Prophet" it states explicitly Eliyahu will announce his arrival first,What is it about ELiyahu Hanavi that the Rambam disagrees with the Gemara and what seems to be an open Posuk that he says it is not for sure he will come first?
The Rambam (Melachim uMilchamot 12:2) does in fact mention this:
There are some Sages who say that Elijah's coming will precede the coming of the Mashiach. All these and similar matters cannot be definitely known by man until they occur for these matters are undefined in the prophets' words and even the wise men have no established tradition regarding these matters except their own interpretation of the verses. Therefore, there is a controversy among them regarding these matters.