fn:max (Section 15.4.3) says that all the items to be compared must be 
convertible to a type that has a gt operator, but the actual definition of the 
function depends on ge, not gt. Similarly, fn:min (Section 15.4.4) says that 
the function depends on the lt operator, but the actual definition depends on 
le, not lt. Suggestion: state that items to be compared must have a ge (le) 
operator, not a gt (lt) operator.