Rationale:

There are two ways to fix the defect; change the description to b-a or change the return to distance(b,a). The LWG preferred the former for consistency.

Proposed resolution:

On the last line of paragraph 9 of section [algorithms] change "a-b" to "b-a".

In paragraph 9 of section [algorithms], it is written:

In the description of the algorithms operators + and - are used for some of the iterator categories for which they do not have to be defined. In these cases the semantics of [...] a-b is the same as of

     return distance(a, b);