How to prove truncated MD (or chop MD) hash function is collision resistant? We have a collision resistant hash function (based MD construction) H with 2n bits hash value size. 
Call chop(H) is a chopping n-bits from H's hash output. 
How can I prove a chop(H) is collision resistant with n-bit?
How to prove a chop(H) is collision resistant with n-bit?


Is this statement true?  Is it true that all collision resistant hash functions remain collision resistant after chopping?

As a hint, you might want to consider this question.