One of the two old chestnuts in the garden happened to crack from the top of its trunk on about one meter... It wasn't visible from my windows and around it, but in plain sight from my neighbour David's. He warned me and kindly offered to take care of it, ie pruning the high branches and shortening the trunk so as to avoid an accident. In case of a storm it could have fallen on his garage, or the other way over my veranda. And he's going to take care of the dead wood. That's good to have such a reliable neighbour! A true European, his mom was Scot, his dad Swedish, and he married a Britton... Thank you David!
Here's what he cut (and the remaining trunk):



And the higher part of the trunk, see the gap...