Jacobi was a mathematician and his "Umkehrfunktion" is in english "Inverse function". It also seems the common english translation: https://www.google.com/s

Jacobi was a mathematician and his "Umkehrfunktion" is in english "Inverse function". It also seems the common english translation: https://www.google.com/search?q=invert+always+invert https://www.google.com/search?q=invert+always+invert To be fair though: While his Wikipedia entry has the sentence: > He is said to have told his students that when looking for a research topic, one should 'Invert, always invert' ('man muss immer umkehren'), reflecting his belief that inverting known results can open up new fields for research, for example inverting elliptical integrals and focusing on the nature of elliptic and theta functions.[8] https://en.wikipedia.org/wiki/Carl_Gustav_Jacob_Jacobi#Scientific_contributions https://en.wikipedia.org/wiki/Carl_Gustav_Jacob_Jacobi#Scien... The attributed source for that, a paper from 1916, differs in the translation: https://www.ams.org/journals/bull/1916-23-01/S0002-9904-1916-02863-1/S0002-9904-1916-02863-1.pdf https://www.ams.org/journals/bull/1916-23-01/S0002-9904-1916... > The great mathematician Jacobi is said to have inculcated upon his students the dictum: Man muss immer umkehren. One must always seek a converse, turn a thought the other end to.