ecq returned to his letter-writing. Then,
stretching out his arm, he made some marks on a white writing-tablet, at
the end of his desk, and rested it against the desk, as though he wished
to keep it in sight. The marks were figures; and Lupin was able to read
the following subtraction-sum:

"9 - 8 = 1"

And Daubrecq, speaking between his teeth, thoughtfully uttered the
syllables:

"Eight from nine leaves one... There's not a doubt about that," he
added, aloud. He wrote one more letter, a very short one, and addressed
the envelope with an inscription which Lupin was able to decipher when
the letter was placed beside the writing-tablet:

"To Monsieur Prasville, Secretary-general of the Prefecture of Police."

Then he rang the bell again:

"Clemence," he said, to the portress, "did you go to school as a child?"

"Yes, sir, of course I did."

"And were you taught arithmetic?"

"Why, sir..."

"Well, you're not very good at subtraction."

"What makes you say that?"

"Because you don't know that nine minus eight equals one. And that, you
see, is a fact of the highest importance. Life becomes impossible if you
are ignorant of that fundamental truth."

He rose, as he spoke, and walked round the room, with his hands behind
his back, swaying upon his hips. He did so once more. Then, stopping at
the dining-room, he opened the door:

"For that matter, there's another way of putting the problem. Take
eight from nine; and one remains. And the one who remains is here, eh?
Correct! And monsieur supplies us with a striking proof, does he not?"

He patted the velvet curtain in which Lupin had hurriedly wrapped
himself:

"Upon my word, sir, you must be stifling under this! Not to say that
I might have amused myself by sticking a dagger through the curtain.
Remember Hamlet's madness and Polonius' death: 'How now! A rat? Dead,
for a ducat, dead!' Come along, Mr. Polonius, come out of your hole."

It was one of those positions to which Lupin was not accustomed and
which he loathed. To catch others in a trap and pull their leg was all
very well; but it was a very different thing to have people teasing him
and roaring with laughter at his expense. Yet what could he answer back?

"You look a little pale, Mr. Polonius... Hullo! Why, it's the
respectable old gentleman who has been hanging about the square for some
days! So you belong to the police too, Mr. Polonius? There, there, pull
yourself together, I sha'n't hurt you