The negator m´eiy˘ou can be used without y˘ou when negating a completed event. For instance, the meaning of the two sentences 他昨天沒有來 (tā zuó tiān méi yǒu lái/ He did not come yesterday.) and 他昨天沒來 (tā zuó tiān méi lái) are exactly the same.
However, 沒有 (m´eiy˘ou) cannot be shortened to 沒 (m´ei) if the negation marker is placed to negate an existential sentence. For example, 有 (y˘ou) cannot be omitted in the sentence 我沒有很多書 (w˘o m´ei y˘ou h˘en-du¯o sh¯u/ I do not have many books.) because it functions as the predicate of an existential sentence.
Reference: Chinese: a linguistic introduction by Chao Fen Sun
