I have a following code to align a system of equations:
\begin{aligned}
& \|\partial_{j_1} \cdots \partial_{j_m} f (a)- \partial_{j_1} \cdots \partial_{j_m} f (x) \|\\
={}& \| \partial^m f (a) \left [e_{j_1}, \ldots, e_{j_m}\right ] - \partial^m f (x) \left [e_{j_1}, \ldots, e_{j_m}\right ]\| \\
={}& \left \| \big ( \partial^m f (a) - \partial^m f (x) \big) \left [e_{j_1}, \ldots, e_{j_m}\right ] \right \| \\
\le{}& \| \partial^m f (a) - \partial^m f (x)\| \cdot \| e_{j_1} \| \cdots \| e_{j_m} \| \\
={}& \| \partial^m f (a) - \partial^m f (x)\|
\end{aligned}
with the result
Could you please explain why the norm symbols || (the third one) are not aligned in this situation? Thank you so much!
\left \right
that is adding the space. (Please always post a complete document to make it easier for people to run the code, it is harder to debug a fragment)