On Friday the dollar closed above its long-run trend for the first time since 29 July. We measure that against the average of the last 200 sessions, and the margin was 0.13%, about as thin as a crossing gets. It had spent the 35 sessions before that underneath the line.

Bitcoin closed Thursday at $76,409. It closed Monday at $86,662, up 13.4% in four sessions, the sharpest four-day rise since the middle of August. Ether rose 13.9% over the same four days, and the rest of crypto rose 14.0% to $560.1 billion, the highest we have seen since we started counting it in June.

You've had the explanations: spot buyers did it, the people betting on a fall got squeezed out, and a Fed that just raised rates and said it would raise again has apparently stopped mattering to the price. It's the third of those we have a stake in, because we wrote the opposite down in June.

The rule, as we've printed it since June: crypto doesn't sustain a rally while the dollar sits above its long-run trend, and the turn comes when the dollar closes back under that line and stays there. We didn't invent it for the summer. A dearer dollar makes everything priced in dollars worth less to everyone who doesn't earn them, and bitcoin is priced in dollars and earns nothing.

For most of the summer the rule held. The dollar went under its trend on 30 July, and across the 35 sessions it stayed there bitcoin rose from $63,724 to $76,409, a gain of about 20%. The dollar moved first and crypto followed, which is the order the rule predicts.

Then on Friday the dollar crossed back over, and bitcoin put on 13% in the four sessions that followed. By our own rule that rise shouldn't hold. So far it has.

On Friday we told you this view was expiring, because the dollar had been under its line since the end of July. Four days later the dollar has gone the other way and the price hasn't noticed. So either the rule is wrong, or four sessions is too few to say, and we can't move the June call until we know which.