S1 and
S2 differ only
in their qualification conversion (
[conv.qual]) and
yield similar types
T1 and
T2, respectively
(where a standard conversion sequence that is a reference binding
is considered to yield the cv-unqualified referenced type),
where
T1 and
T2 are not the same type, and
const T2 is reference-compatible with
T1 (
[dcl.init.ref])
.