The Latin name, meaning ‘bridge of asses’, familiarly given to the fifth proposition in the first book of Euclid’s Elements: that the base angles of an isosceles triangle are equal. It is said to be the first proof found difficult by some readers.
Philosophy
The bridge of asses. Traditionally it is hard to get asses to cross a bridge. In mathematics, the term is applied to the problem from the first book of Euclid that if two sides of a triangle are equal then the angles opposite those sides are also equal. Syllogistic logic had its own pons asinorum: the inventio medii.