I've been working with sets of strings extensively (from the sets module, not the builtin kind), and just tried to replace them with critbit trees as I was curious if they'd be faster. I tested the resulting set cardinalities using the same surrounding logic, and only calling incl/excl on the sets, and strangely found they were close but not exactly the same between the two implementations. Are there any gotchas related to these modules that might have caused this difference? I noticed initSet has a default size parameter where there is no init function for critbits - might this be the culprit? Do I have to somehow clear set contents before I start inserting into them?