 This situation, in which new interaction rules between the connectives arise, is arguably undesirable. In fact, it contradicts a basic criterion of fibring (and also of fusion), as expressed in Gabbay 1999: given logic systems \({{\cal L}}_1\) and \({{\cal L}}_2\), the combination of \({{\cal L}}_1\) and \({{\cal L}}_2\) should be the smallest logic system in the combined language which is a conservative extension of both \({{\cal L}}_1\) and \({{\cal L}}_2\).