Baaxad

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

$F:U\to ℝ$

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

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

Meel walba:

$\mathrm{\nabla }F\ne 0$