Nottingham, an attractive and thriving town in the English Midlands, is famous for its association with Robin Hood, whose statue stands in the shadow of the castle wall. The Sheriff of Nottingham still has a special role in the city government although happily no longer strikes terror into the hearts of the good citizens.

Recently a new attraction, a windmill, has appeared on the Nottingham skyline (see figure 1). The sails turn on windy days and the adjoining mill shop sells packets of stone ground flour but also, more surprisingly, tracts on mathematical physics. The connection between the flour and the physics is part of the mill’s unique character and is explained by a plaque once attached to the side of the mill tower that said,

That is the Green of Green’s theorem, which is familiar to physics undergraduate students worldwide, and of the Green functions that are...

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