https://users.fmf.uni-lj.si/kosir/poucevanje/linalg.html
Linearne enačbe: https://jankoslavic.github.io/pypinm.io/sistemi-linearnih-enacb-2.html
http://web.archive.org/web/20190318180545/https://people.math.carleton.ca/~kcheung/math/notes/MATH1107/wk11/11_surjection_injection_bijection.html
https://people.math.carleton.ca/~kcheung/math/notes/MATH1107/index.html