The compatibility of relevance and mingle (Q1106195)

The very much publishing but nevertheless essentially esoteric group of ``relevant logic'' (especially Belnap, Anderson) poses ``logical'' problems that arise only if we completely forget the primarily semantical character of logic. Thus the problem given in the paper can be formulated as follows: Can the so-called ``mingle axiom'' \(A\to (A\to A)\) be added to a ``relevant system'' without violating ``relevance''? The author tediously proves that it is possible.