[amelius]

And I thought this was about tensor analysis :)

https://en.wikipedia.org/wiki/Covariance_and_contravariance_...

[ttflee]

And it was generalised in category theory:

> The use of both terms in the modern context of multilinear algebra is a specific example of corresponding notions in category theory.

[DonaldFisk]

It's a new meaning for me too. I knew General Relativity before I could program.