Baaxad

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

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

marka $U$ iskajara $S$ bar mucayin ah oo $F$ baaba'da:

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

Meel walba:

$\nabla F\neq 0$