MOM'S SECRET ROOM

[ONEBGG]

In the old days of the cold war, when it was very hard for Westerners to visit the Soviet Union, a British mathematician travels to Moscow to speak in the seminar of a famous Russian professor.
He starts his talk writing a theorem on the board. When he wants to prove it, the professor interrupts him: "This theorem is clear!"
The speaker is, of course, annoyed, but manages to conceal it. He continues his talk with a second theorem, but, again, when he wants to start with the proof, he is interrupted by his host: "This theorem is also clear!"
With a stern face, he writes a third theorem on the board and asks: "Is this theorem clear, too?!"
His host nods.
The visitor grins and says: "This theorem - is false..."