Premise: In London around 11am the march assembles on Camberwell Green. About 250 people are here, from many parts of Britain; I meet marchers from Newcastle, Manchester, Leicester, and especially organized-labor stronghold Sheffield. The sky is grey but the atmosphere is convivial; five members of London's Metropolitan Police are present, and they're all smiling. Most marchers are young, some as young as high school age, but a few are older; some teachers, including members of the Lewisham and Sheffield chapters of the National Union of Teachers, are carrying banners in support of their students.
Hypothesis: The sky is not blue.