Mr. Fisher is a night watchman in a large company. On a certain morning when Mr. Fisher wants to go home, his boss tells him: "I'll go for a businesstrip to Norway. Tomorrow I will depart from Heathrow airport." Mr. Fisher however advises him to take a boat. "Why should I?" asked the president. "This night I dreamed that the plane to Norway crashes, just before it will land," is the response. The president smiles first, but since he is pretty superstitious he decides to take the boat. When he arrives in Norway, he is told that the plane which he should have taken had crashed. When the president returns from the trip, he gives a big reward to Mr. Fisher and immediately fires him. Why?

A renowned and also atlethic rope thief arrives at a tower. Inside this tower two ropes with equal length are hanging downwards from the ceiling. The ropes are connected to the ceiling with rings. How can the thief steal as much rope as possible? The only equipment he carries is a knife.

In a suburb three new houses all have to be connected to a gas (red), water (blue) and electricity (green) supply. All houses should get their own gas, water and electricity connection. Furthermore no connections may cross each other. Because of the danger of stealing, no connections are laid below a house. In the figure on the right-hand side the situation is sketched. The red squares are the houses, the circles the point from which the connections should go to the houses. Why is it impossible to lay down all connections in such a way that no connection crosses another connection?