Bn(a⃗,r)={x⃗ ∣ x⃗∈Rn,∣∣x⃗−a⃗∣∣<r}B^n(\vec{a},r) = \Big\lbrace \vec{x}\ |\ \vec{x} \in \mathbb{R}^n, ||\vec{x} - \vec{a}|| < r\Big\rbraceBn(a,r)={x ∣ x∈Rn,∣∣x−a∣∣<r} then: limx→af(x)=A =def ∀ϵ>0, ∃δ>0, s.t. Bn(a⃗,δ)\{a⃗}⊂f−1(Bn(A,ϵ)) \lim_{x \to a}f(x)=A\ \ \ \stackrel{\mathrm{def}}{=}\ \ \ \forall\epsilon>0,\ \exist \delta > 0,\ s.t.\ \ B^n(\vec{a},\delta) \backslash \big\lbrace \vec{a} \big\rbrace \subset f^{-1}(B^n(A,\epsilon))x→alimf(x)=A =def ∀ϵ>0, ∃δ>0, s.t. Bn(a,δ)\{a}⊂f−1(Bn(A,ϵ))
