essions should be the
    same), and (b) that the return types of the operators should follow
    semantics of return types of corresponding operators for built-in types
    (<i>e.g.</i> <code>operator&lt;</code> should return a type convertible
    to <code>bool</code>, and <code>T::operator-=</code> should return type
    convertible to <code>T</code>). Such "loose" requirements make operators
    library applicable to broader set of target classes from different
    domains, <i>i.e.</i> eventually more u