<p><b>Post-finalization note 3</b>:

The "Comparator restrictions" section of this SRFI states that

implementations must not require comparators used to create

sets or bags to have both an ordering predicate and a hash

function.  However, in practice this is a nullity, because there

is no way to determine which type of procedure the implementation

requires, and therefore users must supply both procedures.  Now that

<a href="http://srfi.schemers.org/srfi-153/srfi-153.html">SRFI 153</a>

(in draft status at the time of this writing) requires comparators

with ordering predicates, the author of this SRFI strongly urges

implementers to accept comparators with hash functions with or

without ordering predicates. The sample implementation,

which is built on top of hash tables, already does so.</p>