"Uh huh." I grinned at him. "What about my hotel?"

"I'll show you. Look through that window. See the street lamp?"

"Vaguely."

"You bet, vaguely. San Francisco is a town with an active history. The world lines are constantly merging. What you're looking at is the probability of a street lamp being in a particular place. Looks like a big fuzzy ball, doesn't it? That's the locus of points where a bulb might be

—or a gas flame. Greatest probability density is in the center, where it shows brightest."

"I don't get it."

"When the world lines merge, everything blurs. The further away something is, the more blurred it looks. I shouldn't say looks, because the blurring is real; it's no illusion. Can you see your hotel from here?"

I looked out the appropriate window, and I couldn't. Two hours ago I'd nearly lost my way just crossing the street. Tonight a man could lose himself in any city street, and wander blindly in circles in hopes of finding a curb. .

"You see? Your hotel's too far away. In the chaos out there, the probability of your hotel being anywhere specific is too small to see. Vanishingly small. You'd never make it."

Something about the way he talked…

"I wondered when you'd notice that." He smiled as if we shared a secret.

"All this time," I said, "I've been thinking that you talk just like everyone else. But you don't. It's not just the trace of accent. Other people don't say probability density or theorem or on the order of."

"No, they don't."

"Then we must both be mathematicians!" I smiled back at him.

"No," he said.

"But then..." But 1 backed away from the problem, or from the answer. "My glass is empty. Could you use a refill?"

"Thanks, I could."

I fixed it with the bartender. "Funny thing," I told the brown-haired man. "I always thought the blurring effect of fog came from water droplets in the air."

"Bosh," he said. "Bosh and tish. The water's there, all right, whenever the fog rolls in. I can't explain it. The condensation must be a side effect from the blurring of the world lines. But that's not interfering with your vision. Water's transparent."

"Of course. How could I have forgotten that?"

"I forgot it myself, a long time ago." The scotch was beginning to reach him, I think. He had an accent, and it was growing stronger. "That's why I'm here. That's why I stopped you. Because you'd remember."

The bartender brought us our drinks. His big shoulders were hunched inward against the damp gray light that seeped in the windows.

I sipped at the burning hot glass. Irish whiskey and strong black coffee poured warmth through me, to counteract the cold beyond the walls. A customer departed, and the fog swirled around him and swallowed him.

"I walked into the fog one afternoon," said the brown-haired man. "The fog was thick, like tonight. A cubic mile of cotton, as we say. I was just going out for a pouch of snuff. When I reached the tobacconist's he tried to sell me a bundle of brown paper sticks with a Spanish trademark."

"Uh huh. What did you do?"

"Tried to get home, of course. Things changed oddly while I wandered in the fog. When it cleared and left me stranded, even my money was no good. The worst of it was that I couldn't even tell my story. Nobody could read my mind to see that I was sane. It was find another fog bank or try to make a life for myself."

"With no money?"

"Oh, I sold my ring and found a poker game."

"Oh. Oh!"

"That was a year ago. It's worked out well enough. I thought I might invent something, like the zipper, but that fell through. You're far ahead of us in the physical sciences. But money's no problem. Sometimes there's a fixed horse race. Sometimes I find a poker game, or a crooked crap game where they'll let me bet the right way."

"Sounds great." But not very honest, I thought.

"You disapprove?" My companion's voice had gone thin and cold.

"I didn't say that."

"I compensate for what I take," the brown-haired man said angrily. "I know how to untwist a sick man's mind. If a player sits down with emotional problems, I can help him. If he really needs the money, I can see that it comes to him."

"Why don't you become a psychiatrist?"

He shook his head. "It would take years, and then I'd never be able to hold a patient long enough to do myself any good. He'd get well too fast. Besides that, I hate certain people; I'd want to harm them instead of helping them. .

"Anyway, I don't go out in the fog anymore. I like it here. I stopped you because you're one of those who remember."

"You said that before. What exactly—?"

"After all, people are constantly walking into fogs. Why is it that we don't hear more about people wandering in from alternate world lines? It's because their memories adjust."

"Ah."

"I caught it happening once. A girl from somewhere else... I didn't catch the details; they faded too fast. I got her a job as a go-go dancer. I think she was a prize concubine in someone's harem before she ran into the fog.

"Their memories adjust. They forget their friends, their relatives, their husbands and wives in the old world line. They remember what man is king or president or chairman in the new. But not us. You and I are different. I can recognize the rare ones."

"Because you can read minds." Sarcastically. Part of me still disbelieved; yet... it fit too well. The brown-haired man talked like a mathematics professor because he was talking to me, and I was a mathematics professor, and he was reading my mind.

He looked thoughtfully into his glass. "It's funny, how many sense the truth. They won't walk or drive in the fog if they can help it. At the bottom of their minds, they know that they might return home to find a Romish camp, or a Druidic dancing ground, or the center of a city, or a sand dune. You knew it yourself. The top of your mind thinks I'm an entertaining liar. The deepest part of you knew it all before I spoke."

"I just don't like fog," I said. I looked out the window, toward my hotel, which was just across the street. I saw only wet gray chaos and a swirling motion.

"Wait until it clears."

"Maybe I will. Refill?"

"Thanks."

Somehow, I found myself doing most of the talking. The brown-haired man listened, nodded occasionally, asked questions from time to time.

We did not mention fog.

"I need an ordered universe," I said at one point. "Why else would I have studied math? There's never an ambiguity in mathematics."

"Whereas in interpersonal relationships..."

"Yes! Exactly!"

"But mathematics is a game. Abstract mathematics doesn't connect with the real universe except by coincidence or convenience. Like the imaginary number system: it's used in circuit design, but it certainly wasn't intended for that."

"No, of course not."

"So that's why you never got married?"

"Right," I said sadly. "Ordered universe. Hey, I never knew that. Did I?"

The fog cleared about one o'clock. My brown-haired friend accompanied me out.

"Mathematics doesn't fit reality," he was saying. "No more than a game of bridge. The real universe is chaotic."

"Like in-ter-personal re-lationships."

"Maybe you'll find them easier now."

"Like fog. Well, maybe I will. I know some new things about myself Where's my hotel?"

There was no hotel across the street.

Suddenly I was cold sober, and cold scared.

"So," said my drinking partner. "You must have lost it earlier. Was it foggy when you crossed?"

"Thick as paste. Oh, brother. Now what do I do?"

"I think the fog's starting to roll in again. Why not wait? The bar won't close until four."

"They close at two in my world." In my world. When I admitted that, I made it real.