The policeman closes the door to my office, then sits in the chair Mr. Aldrin placed for him. I sit down behind my desk. He is looking around the room.
“You like things that turn around, don’t you?” he says.
“Yes,” I say. I wonder how long he will stay. I will have to make up the time.
“Let me explain about vandals,” he says. “There’s several kinds. The person — usually a kid — who just likes to make a little trouble. They may spike a tire or break a windshield or steal a stop sign — they do it for the excitement, as much as anything, and they don’t know, or care, who they’re doing it to. Then there’s what we call spillover. There’s a fight in a bar, and it continues outside, and there’s breaking windshields in the parking lot. There’s a crowd in the street, someone gets rowdy, and the next thing you know they’re breaking windows and stealing stuff. Now some of these people are the kind that aren’t usually violent — they shock themselves with how they act in a crowd.” He pauses, looking at me, and I nod. I know he wants some response.
“You’re saying that some vandals aren’t doing it to hurt particular people.”
“Exactly. There’s the individual who likes making messes but doesn’t know the victim. There’s the individual who doesn’t usually make messes but is involved in something else where the violence spills over. Now when we first get an example of vandalism — as with your tires — that clearly isn’t spillover, we first think of the random individual. That’s the commonest form. If another couple cars got their tires slashed in the same neighborhood — or on the same transit route — in the next few weeks, we’d just assume we had a bad boy thumbing his nose at the cops. Annoying, but not dangerous.”
“Expensive,” I say. “To the people with the cars, anyway.”
“True, which is why it’s a crime. But there’s a third kind of vandal, and that’s the dangerous kind. The one who is targeting a particular person. Typically, this person starts off with something annoying but not dangerous — like slashing tires. Some of these people are satisfied with one act of revenge for whatever it was. If they are, they’re not that dangerous. But some aren’t, and these are the ones we worry about. What we see in your case is the relatively nonviolent tire slashing, followed by the more violent windshield smashing and the still more violent placement of a small explosive device where it could do you harm. Every incident has escalated. That’s why we’re concerned for your safety.”
I feel as if I am floating in a crystal sphere, unconnected to anything outside. I do not feel endangered.
“You may feel safe,” Mr. Stacy says, reading my mind again. “But that doesn’t mean you are safe. The only way for you to be safe is for that nutcase who’s stalking you to be behind bars.”
He says “nutcase” so easily; I wonder if that is what he thinks of me as well.
Again, he reads my thoughts. “I’m sorry — I shouldn’t have said ‘nutcase.’… You probably hear enough of that sort of thing. It just makes me mad: here you are, hardworking and decent, and this — this person is after you. What’s his problem?”
“Not autism,” I want to say, but I do not. I do not think any autistic would be a stalker, but I do not know all of them and I could be wrong.
“I just want you to know that we take this threat seriously,” he says. “Even if we didn’t move fast at first. So, let’s get serious. It has to be aimed at you — you know the phrase about three times enemy action?”
“No,” I say.
“Once is accident, twice is coincidence, and third time is enemy action. So if something that only might be aimed at you happens three times, then it’s time to consider someone’s after you.”
I puzzle over this a moment. “But… if it is enemy action, then it was enemy action the first time, too, wasn’t it? Not an accident at all?”
He looks surprised, eyebrows up and mouth rounded. “Actually — yeah — you’re right, but the thing is you don’t know about that first one until the others happen and then you can put it in the same category.”
“If three real accidents happen, you could think they were enemy action and still be wrong,” I say.
He stares at me, shakes his head, and says, “How many ways are there to be wrong and how few to be right?”
The calculations run through my head in an instant, patterning the decision carpet with the colors of accident (orange), coincidence (green), and enemy action (red). Three incidents, each of which can have one of three values, three theories of truth, each of which is either true or false by the values assigned each action. And there must be some filter on the choice of incidents, rejecting for inclusion those that cannot be manipulated by the person who may be the enemy of the one whose incidents are used as a test.
It is just such problems I deal with daily, only in far greater complexity.
“There are twenty-seven possibilities,” I say. “Only one is correct if you define correctness by all parts of the statement being true — that the first incident is in fact accident, the second is in fact coincidence, and the third is in fact enemy action. Only one — but a different one — is true if you define correctness as all three incidents being in fact enemy action. If you define correctness as the third incident being enemy action in all cases, regardless of the reality of the first two cases, then the statement will correctly alert you to enemy action in nine cases. If, however, the first two cases are not enemy action, but the third is, then the choice of related incidents becomes even more critical.”
He is staring at me now with his mouth a little open. “You… calculated that? In your head?”
“It is not hard,” I say. “It is simply a permutation problem, and the formula for permutations is taught in high school.”
“So there’s only one chance in twenty-seven that it is actually true?” he asks. “That’s nuts. It wouldn’t be an old saw if it wasn’t truer than that… that’s what? About four percent? Something’s wrong.”
The flaw in his mathematical knowledge and his logic is painfully clear. “Actually true depends on what your underlying purpose is,” I say. “There is only one chance in twenty-seven that all parts of the statement are true: that the first incident is an accident, the second incident is a coincidence, and the third incident is enemy action. That is three-point-seven percent, giving an error rate of ninety-six-point-three for the truth value of the entire statement. But there are nine cases — one-third of the total — in which the last case is enemy action, which drops the error rate with respect to the final incident to sixty-seven percent. And there are nineteen cases in which enemy action can occur — as first, second, or last incident or a combination of them. Nineteen out of twenty-seven is seventy-point-thirty-seven percent: that is the probability that enemy action occurred in at least one of the three incidents. Your presumption of enemy action will still be wrong twenty-nine-point-sixty-three percent of the time, but that’s less than a third of the time. Thus if it is important to be alert to enemy action — if it is worth more to you to detect enemy action than to avoid suspecting it when it does not exist — it will be profitable to guess that enemy action has occurred when you observe three reasonably related incidents.”
“Good God,” he says. “You’re serious.” He shakes his head abruptly. “Sorry. I hadn’t — I didn’t know you were a math genius.”
“I am not a math genius,” I say. I start to say again that these calculations are simple, within the ability of schoolchildren, but that might be inappropriate. If he cannot do them, it could make him feel bad.
“But… what you’re saying is… following that saying means I’m going to be wrong a lot of the time anyway?”