Haha. Now that you mention you're right but this would add a requirement on algebra to import that type right? Right now this module only depends on core and would need a separate package to bring in Mergable and friends. 

Re: the Int comment. Great point haha. I generally think of the common use case with Counters. The default being increment by one but a batched operation could potentially increment by alot, a `Long` lot in twitters case :)