Euler–Lagrange equations and Noether's theorem . "The cool thing is that this way of thinking about physics has survived some major revolutions in physics, like quantum mechanics, relativity, etc.

A butterfly is a mainly day-flying insect of the order Lepidoptera, which includes the butterflies and moths

Go Luna Girl: Emmy Noether In Albert Einstein wrote a letter to the New York Times, praising Emmy Noether as “the most significant creative mathematical genius thus far produced since the higher education of women began.

Noether's Theorems ( Atlantis Studies in Variational Geometry) (Hardcover)