Deng Xiaoping's contributions to Reform and Opening Up cannot be overlooked.
Tips
usage
Literally "merit (功) cannot (不可) be erased (没)." 没 here is read mò "to drown/efface," not méi. The idiom is used to give explicit credit, often when summing up someone's role in a collective achievement.
mistakes
Don't read 没 as méi here — it's mò ("to submerge/erase"). Reading 功不可méi would change the sense to "merit cannot be lacking," which is wrong.