  This scheme states that something is obligatory if and only if it is the case. In other words, in Mally’s system, the obligatory and the factual collapse. This, of course, is unacceptable. The first one to show this was Karl Menger in 1939. Further discussion of Mally’s deontic logic can be found in Morscher 1998, as well as in the entry cited above, i.e., Lokhorst 2013a. We would like to reiterate Lokhorst’s claim that despite the flaw in Mally’s deontic logic, his “pioneering effort deserves rehabilitation rather than contempt”. See also Lokhorst’s papers on an intuitionistic reformulation of Mally’s deontic logic, where he tries to capture Mally’s basic ideas whilst avoiding the collapse referred to above (Lokhorst 2013b and 2015).