The Super Computer stood at the end of the Computer Company's production line. At which point the guided tour eventually arrived. The salesman stepped forward to give his prepared demo.
"This", he said, "is the Super Computer. It will give an intelligent answer to any question you may care to ask it".
At which a Clever Guest stepped forward - there is always one - and spoke into the Computer's microphone.
"Where is my father?" he asked.
There was a whirring of wheels and flashing of lights that the manufacturers always use to impress lay people, and then a little card popped out.
On it were printed the words: Fishing off Goa.
Clever Guest laughed.
"Actually", he said, "My father is dead"!
It had been a tricky question! The salesman, carefully chosen for his ability to think fast on his feet, immediately replied that he was sorry the answer was unsatisfactory, but as computers were precise, perhaps he might care to rephrase his question and try again?
Clever Guest thought, went to the Computer and this time said, "Where is my mother's husband?"
Again there was a whirring of wheels and a flashing of lights. And again a little card popped out. Printed on it were the words, "Dead. But your father is still fishing off Goa."