91av

The "ultrafinitists" who seek to abolish the use of infinity in mathematics reminded me of the influential Dutch mathematician L. E. J. Brouwer, renowned for proving Brouwer's fixed-point theorem. He went on to found an approach to mathematics that he called intuitionism, which included a rejection of the concept of actual infinity, though it admitted …

You report research that says smartphone use on the toilet may increase the risk of haemorrhoids by nearly 50 per cent. That leaves me to assume, or at least hope, that crosswords and printed magazines are more benign( 13 September, p 10 ).

With reference to your article "Smartphone use on the toilet may raise risk of haemorrhoids", I am left wondering whether reading the print version of 91av on the toilet carries the same risk? Or is it only if I read it via the app on a smartphone? More research is required!

During the Little Ice Age, temperatures dropped by an average of up to 1.75°C, or 3.15°F ( 6 September, p 11 ). The term atrox is a Latin word meaning fierce ( 6 September, p 14 ).

With the recent news of some possible signs of ancient life on the Martian surface, there will naturally follow the usual comments – that even if there were any life long ago, there won't be any living now, due to the hostile surface conditions( 20 September, p 12 ). However, once life started on Earth, …

Fortunately, there are more ways to store carbon dioxide than just underground. Trees and other plants also store it and when we use them to, say, build high-rise buildings or furniture, or make car parts (flax and hemp can be used in door panels and dashboards), we store CO 2 for years, and possibly for …

When it comes to the phrase space-time, Chanda Prescod-Weinstein ponders what is in a hyphen? Space answers to the question "where?", time to the question "when?". Space-time answers to the question "when and where?". "Spacetime" answers to no question at all. It is a new concept that needs a lot of explaining ("what?") and probably …

Robert Sugden says otroverts, people who naturally don't conform to groups, will never form their own groups for the obvious reason. But a few decades ago, people would have said the same about autistic people. Yet since the arrival of the internet, they have formed online groups to share experiences, developing guidelines that have since …

Sugden's witty letter about being an otrovert prompted me to reread Rami Kaminski's original article. I happened to be stroking my cat, whom I respect and admire, at the time, and it struck me that cats are extreme otroverts, the polar opposite to dogs. Our cat exploits us mercilessly, while being totally indifferent to our …

How to make it to 100? I'm determined to live to 200. Or die trying( 20 September, p 36 ).