The type of the hashtable keys.

The equality predicate used to compare keys.

A hashing function on keys. It must be such that if two keys are equal according to equal, then they have identical hash values as computed by hash. Examples: suitable (equal, hash) pairs for arbitrary key types include ((=), Hashtbl.hash) for comparing objects by structure, ((fun x y -> compare x y = 0), Hashtbl.hash) for comparing objects by structure and handling Pervasives.nan correctly, and ((==), Hashtbl.hash) for comparing objects by addresses (e.g. for cyclic keys).