This is a question related to formatting. I have an expression that is equal to zero; I work over this expression to obtain a final relation as shown below:
$$\begin{align*} 0 & =\int_{V}\nabla\cdot\mathbf{A}\,\mathrm{d}V\\ & =\int_{S}\mathbf{A}\cdot d\mathbf{S}\\ & =\int_{S}\mathbf{\hat{n}}\cdot\mathbf{A}\,d\mathit{S}\\ & =\left(\mathbf{A}_{i}-\mathbf{A}_{e}\right)\cdot\mathbf{\hat{n}} \end{align*}$$
My question is: is it correct formatting to leave the zero in the left hand side? I have searched for answers but I could not find it. Thanks in advance.