Baaxad

Qayb ka mid ah laamaha ${\displaystyle S}$ Saddex baaxadood leh ${\displaystyle \mathbb {R} ^{3}}$ Waa baaxad ee loogu talo galay bar kasta ${\displaystyle x}$ ka kooban ${\displaystyle S}$ meelo furan ${\displaystyle U}$ shaqooyin kala duwan

${\displaystyle F:U\to \mathbb {R} \,\!}$

marka ${\displaystyle U}$ iskajara ${\displaystyle S}$ bar mucayin ah oo ${\displaystyle F}$ baaba'da:

${\displaystyle U\cap S=F^{-1}(0)}$

Meel walba:

${\displaystyle \nabla F\neq 0}$