But it seemed the only answer. Every time I changed the past, I was creating an alternate world—

My head was starting to hurt.

Now, wait a minute — I had already changed the past! I had worn different clothes and I had given Dan two hundred dollars to bet instead of one hundred. And the newspaper I had brought with me—

The newspaper, of course! It had been staring at me all the time. FIVE-HORSE PARLAY WINS $57,600!

But it wasn’t a five-horse parlay — not anymore! It was only a four-horse parlay! We hadn’t stayed to bet on bet on Michelangelo. We’d doubled the first bet. It was only coincidence that we’d ended up with the same amount.

But the important thing was: I had changed the past. Just as Don had come back in time to change his past, so I had done the same thing to my past, though not on so large a scale. I remembered my past differently — I remembered different clothes, a different bet and a five-horse parlay. I remembered it the way it had happened to me — and then I had changed it.

So where was my Don — the one I had gone to the races with? Where was he?

The situation was exactly the same: I had changed the past and destroyed the future. So where was he?

Well, that was silly. He was me. He hadn’t disappeared — he was right here. I had simply done things differently this time around.

Ouch.

That meant that the Don who had come back in time with the newspaper was me too. (Of course — but would I have to go back in time to warn myself? No, because I hadn’t let the bets go that far.)

Then, if he was me… there really was only one of me! He would go back to the future — my future, our future — with his memories, but—

But if his memories were different than mine, how could we be the same person?

So the question was still unanswered: Where was the Don I had gone to the races with? The one who had worn a sweater and slacks and bet only a hundred dollars? Where was my good sport jacket?!!

Danny showed up then, he was giddy and excited — like he’d invented money. He waved the check at me.

“You want to see it?”

I took it thoughtfully and looked. I took my check out of my pocket and compared them — they were not identical. The check number on Danny’s was lower and the signatures were not quite the same.

Of course, how could they be identical? We were leaving earlier in the day after a different set of bets. The situations were not the same — why should the checks be?

Then, this check I was carrying — it was no longer any good, it was from a world that no longer existed.

And it was the same situation with the disappearing Don; he was a canceled check in this world, wasn’t he?

But the canceled check hadn’t disappeared. I still had it.

(I remembered myself asking if we could cash them both.)

I’d been fooled once by the illusion of the duplicated check, but this time the check had been duplicated!

And if I could duplicate the check, then couldn’t I have duplicated myself?

There was another side to it too.

I’d already eliminated two possible futures: the one where I’d worn slacks and a sweater and the one where I’d won a million and a half dollars.

As far as I knew, both of those Dons had ceased to exist along with their futures. Neither seemed to be still around.

And if I could eliminate them — - what was to keep some other Dan from eliminating me?

Perhaps even now—

No. There must be something I was misunderstanding.

Danny drove. He babbled incessantly; he was like a schoolgirl. But I wasn’t listening anyway. I was too preoccupied with my own thoughts.

I knew there was an answer.

There had to be.

For one thing, paradoxes were supposed to be impossible.

Oh, sure, I know — time travel makes the most horrendous of paradoxes possible, even probable; but that’s just not so. A paradox would be a violation of the laws of nature. By definition, they’re the laws of nature. And inviolable.

Therefore, paradoxes are impossible.

Because if paradoxes were possible, then time travel would have to be impossible — otherwise, we’d have people killing their grandfathers right and left. We’d have people seducing their mothers or kidnapping their fathers. We’d have time travelers killing the inventors of time machines. We’d have all manner of anachronisms and flukes, and the laws of nature would be violated in so many different ways, it would take the invention of a whole new science to catalog them all.

But time travel was possible. I had proved it myself.

So paradoxes were impossible.

It sounded all very neat when I explained it to myself that way. Paradoxes had to be impossible; therefore, they were. Everything could be worked out logically—

Then, dammit, why couldn’t I work this one out? If this wasn’t a paradox, it was still way ahead of whatever was in second place.

All right. Let’s assume that paradoxes are impossible — then where do I go from here?

The checks, for instance. Obviously, Danny’s check was the good one, the one we would have to cash in order to collect our winnings. But the question was how?

Should I take it forward with me into the future? But then what would Danny have to show himself when he was Don? (Of course, I hadn’t made a point of comparing the checks this time around, had I?) But if I left it here in the past, how would I get it in the future?

My check shouldn’t exist. It was from a canceled world. Danny’s check was the only valid one here because I had done things differently from the way they had originally occurred. If I had done things the way Don had done, I would have had the “duplicate” of Danny’s check.

But I hadn’t. I had tampered with the timestream and didn’t have a valid check at all. And that meant—

—that I was a canceled check too.

Because whatever I did now, this Danny — when he became Don and went back in time — would not do exactly the same as me. It would be impossible for him to do so. Just as I had eliminated the Don preceding me, this Danny was going to eliminate the Don preceding him — me!

Did I still exist?

Was I about to wink out?

Was it just a matter of time?

Yes — of course it was a matter of time. Ha, ha. The joke’s on me.

No, this couldn’t be right; I was thinking in paradoxes again. After all, I was here and alive — I was me. I hadn’t eliminated Don at all. I had become him and done things differently, that’s all.

Sure — but I still couldn’t stop asking myself what had become of my Don who had done things the other way and the Don who had given me the newspaper and told me not to be so greedy. ("Forget about them — you simply won’t become them, that’s all,” I told myself. “How would you know?” I answered.)

Let’s see… there must be a way to figure this out.

Danny had to go back in time and become Don to his Dan.

If he takes his check back with him, I won’t have it to cash. On the other hand, if I take it forward with me, he won’t have a check to show his Danny. (He’ll be changing the timestream, just like me. Unless — )

What if I gave Danny the false check to take back with him? Would that undo the damage? Or would it just make it worse?

My mind began to boggle.

But it was the answer, of course. This Danny would become my Don! That’s why his check would match mine when he went back to meet me — (and he’d test to see if he could change the past too! He’d try wearing different clothes than me: the slacks and sweater!)