uctible, <i>etc.</i>), although some of them could
    be; they are what we call <i>concepts with a small 'c'</i>. In
    particular, they are different from the former ones in that they <em>do
    not</em> describe precise semantics of the operators they require to be
    defined, except the requirements that (a) the semantics of the operators
    grouped in one concept should be consistent (<i>e.g.</i> effects of
    evaluating of <code>a += b</code> and
    <code>a&nbsp;=&nbsp;a&nbsp;+&nbsp;b</code> expr