Riddle 1 Answer
I appear to have left Riddle 1 sitting out there without an official answer for almost seven months now. Sorry about that.
The answer given by Peter Byrne was valid, and essentially the one I was thinking of: while his example dealt with the untyped empty list
(), I had the typed empty list
`boolean$() in mind.
The insight here is that
all are forms of
max; and that
min x,y, the min of the concatenation of two lists, is equal to
min(min x;min y), the min of their separate
mins (and mutatis mutandis for
max). For this to work consistently for empty lists, the
min of an empty list must be the maximum possible value for that data type (and mutatis mutandis for