This is technically a riddle, but it makes me
The Omnibombulator
This unusual instrument is operated by selecting one of the four switch-positions A, B, C, D and turning the power on. The effects are;
Position A - The pratching valve glows and the queech obulates
Position B - The queech obulates and the urfer curls up, but the rumption does not get hot.
Position C - The sneeveling rod turns clockwise, the pratching valve glows and the queech fails to obulate.
Position D - The troglodyser gives off hydrogen but the urfer does not curl up.
Whenever the pratching valve glows the rumption gets hot. Unless the
sneeveling rod turns clockwise, the queech cannot obulate, but if the
sneeveling rod is turning clockwise the troglodyser will not emit hydrogen. If the urfer does not curl up you may be sure that the rumption is not getting hot.
In order to get milk chocolate from the machine you must ensure (a) that the sneeveling rod is turning clockwise AND (b) that, if the troglodyser is emitting hydrogen then the pratching valve is glowing, but that if the troglodyser is not emitting hydrogen, the queech is not obulating.
Which switch position would you select?
If, tiring of chocolate, you wish to receive the Third Programme you must take care (a) that the rumption does not get hot AND (b) either the urfer doesn’t curl and the queech doesn’t obulate OR that the pratching valve glows and the troglodyser fails to emit hydrogen,
Which switch position would you select?