There was a pleasant surprise for me in the post the other day. The bi-annual statement detailing how my pension investments are doing showed another hefty gain, as it has done pretty consistently for some years now and as would be the case for more or less everyone who has their pension pot invested substantially in equities. Stock markets have on the whole been doing well for nearly 10 years now, remarkably so when it comes to the US, which is about to enter the record books with the longest bull run in history.

As ever, the question is for how much longer can it last?

I don't want to dwell unduly on the extended duration of the current economic expansion, suffice it to say that it is already exceptional by historic standards. The law of averages alone suggests that it must soon draw to a close, as likely as not ended by Federal Reserve tightening, to the growing frustration of Donald Trump, who told a Republican fundraiser in the Hamptons at the weekend that he thought he had appointed an advocate of cheap money when he made Jay Powell the Fed chairman, but instead finds an independently minded policymaker of apparently hawkish tendency. Like president Recep Erdogan in Turkey, Trump expects a compliant central bank. As it is, it seems ever more probable that Fed tightening is going to shift the global economy into an at best still growing, but fast slowing, disposition.

Yet there are at least four other factors, somewhat divorced from the usual ups and downs of the macro-economy, which are also flashing amber, if not outright red - buyback activity, valuation, computer-driven trading, and the related issue of artificial intelligence, or machine learning.