Is it permissible for the one being led in prayer (ma'mum) to correct the imam if he makes a mistake in his recitation or forgets a verse during a fard (obligatory) prayer?

Opening up to the Imam is of two types: an obligatory opening, which is in matters whose deliberate commission invalidates the prayer, such as distorting the meaning in Al-Fatiha or omitting a verse from it; and a recommended opening, which is in matters that lead to missing perfection, such as forgetting to recite a surah after Al-Fatiha. The proof for this is the Prophet's (peace and blessings be upon him) hadith: "Indeed, I am a human being like you; I forget as you forget. So, if I forget, remind me."