val hash : t -> intA 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
(provided objects do not contain floats)(fun x y -> compare x y = 0), Hashtbl.hash)
for comparing objects by structure
and handling Pervasives.nan correctly(==), Hashtbl.hash) for comparing objects by physical
equality (e.g. for mutable or cyclic objects).