As is common in mathematical fiction written by non-mathematicians the word "equation" here is misused. A formula is not an equation unless it has an equal sign in it! Usually, this is just a matter of terminology, but in this case it is a more serious problem. The mathematical expression that is the key involves absolute values, x's and y's. If one sets this equal to something, it corresponds to some geometric object, a set of lines in the xy-plane that can be graphed. Apparently, this is what the author intended us to imagine. However, without knowing what it is equal to (is it 1? is it 0? or is there an equal sign missing from somewhere in the middle of the expression?) I do not know what it is supposed to be. I tried several possibilities and did not find anything reasonable. Can any of you help me figure out what was intended?

I cannot strongly recommend this story. It is one of a collection of stories by this author, each of which intentionally violates one of the supposed "rules" of mystery fiction. (The rule this one breaks is "No hitherto undiscovered poisons may be used, nor any appliance which will need a long scientific explanation at the end.".) However, this story leads me to wonder whether it would have been better to follow the rules in this case. The jokes are not terribly funny, the mystery not terribly mysterious, and the fact that the main character is a drop-dead beautiful singer from a communist country is not enough to make it interesting. Worst of all, it is full of completely unbelievable coincidences. For me, that completely spoils any "whodunnit".

In any case, I am grateful to Vijay Fafat for bringing this story, imperfect as it may be, to my attention.