I was walking along a pavement in Didsbury, a suburb of Manchester, one summer day more than ten years ago, and pedalling her tricycle along in front of me was a small girl of about three years old. Her parents called to her, from behind me, that she was to wait and not go so far ahead. 'Anna,' they called, 'Anna, wait a bit.' Naturally, I turned round, that being my name also, but it was the diminutive Anna on the triang trike who was being addressed. She paid very little attention to them, but pedalled onward, her long hair hanging loose down her back and over her shoulders so that she made a unified triangular form that would have packed neatly into a tetrahedron. Girl and Tricycle, I thought, as I overtook and passed them, make a three-sided pyramid, and it would be possible to make a clay tetrahedron, standing on one of its plane surfaces, and to add a flat, round-faced head and indications of wheels and handlebars, and madly revolving legs, and she would be a chunk of sculpture.

Even longer ago, at a time when I did a fair bit of worrying about my left-handed son who was slow to acquire fluent speech, I stumbled across some miscellaneous fragments of knowledge concerning left and right cerebral hemispheres, left and right handedness, speech, writing, reading and stuttering. The right hemisphere, so I read, controls the left side of the body and concerns itself with ...