Template:Are You Sure/May 9

A flea circus is a circus sideshow attraction in which fleas are attached (or appear to be attached) to miniature carts and other items, and encouraged to perform circus acts within a small housing.

The Human Flea Circus is "similar, but with people instead of fleas." [citation needed]

• ... that tickets for the Human Flea Circus are being given away free due to COVID-19 lockdown restrictions?

• ... that Jensen's inequality, named after the Danish mathematician Johan Jensen (1859–1925), relates the value of a convex function of an integral to the integral of the convex function; and that in its simplest form the inequality states that the convex transformation of a mean is less than or equal to the mean applied after convex transformation; and that it is a simple corollary that the opposite is true of concave transformations; and that Jensen's inequality generalizes the statement that the secant line of a convex function lies above the graph of the function, which is Jensen's inequality for two points?

• ... that mathematician, cosmographer, and astrologer Paolo dal Pozzo Toscanelli (1397–1482) was one of the central figures in the intellectual and cultural history of Renaissance Florence in its early years, and that his circle of friends included Filippo Brunelleschi (architect of the Duomo) and philosopher Marsilio Ficino; and that Toscanelli knew mathematician and architect Leon Battista Alberti; and Toscanelli's closest friend was Cardinal Nicholas of Cusa, himself a wide-ranging intellect and early humanist, who dedicated two short mathematical works, both written in 1445, to Toscanelli, and made himself and Toscanelli the interlocutors in a dialogue (1458) entitled De quadratura circuli ("On Squaring the Circle")?