  After recalling briefly the main properties of the amalgamated duplication of
a ring $R$ along an ideal $I$, denoted by $R\JoinI$, we restrict our attention
to the study of the properties of $R\JoinI$, when $I$ is a multiplicative
canonical ideal of $R$ \cite{hhp}. In particular, we study when every regular
fractional ideal of $R\Join I$ is divisorial.
