Errors for math equations to print PDF from Jupyter notebook

Hey everyone,

**I write a table in jupyter notebook and declare some usual statistics symbols like Latex.

$\DeclareMathOperator{\Corr}{Corr}$
$\DeclareMathOperator{\Var}{Var}$
$\DeclareMathOperator{\E}{\mathbb{E}}$
$\DeclareMathOperator{\Cov}{Cov}$**

However, when I print it to PDF, it fails. any ideas to fix it? Thank you very much!

Package hyperref Warning: Rerun to get /PageLabels entry.

(c:/texlive/2017/texmf-dist/tex/latex/psnfss/ot1ppl.fd)
(c:/texlive/2017/texmf-dist/tex/latex/psnfss/omlzplm.fd)
(c:/texlive/2017/texmf-dist/tex/latex/psnfss/omszplm.fd)
(c:/texlive/2017/texmf-dist/tex/latex/psnfss/omxzplm.fd)
(c:/texlive/2017/texmf-dist/tex/latex/psnfss/ot1zplm.fd)

LaTeX Warning: No \author given.

(c:/texlive/2017/texmf-dist/tex/generic/oberdiek/se-ascii-print.def)

Package longtable Warning: Column widths have changed
(longtable) in table 1 on input line 314.

! LaTeX Error: Can be used only in preamble.

See the LaTeX manual or LaTeX Companion for explanation.
Type H for immediate help.
...

l.323 Proof: \(\DeclareMathOperator
{\Corr}{Corr}\)
?
! Emergency stop.
...

l.323 Proof: \(\DeclareMathOperator
{\Corr}{Corr}\)
No pages of output.
Transcript written on notebook.log.

Reproduce the reported PDF export with the shown DeclareMathOperator lines and inspect the generated LaTeX around the failing line. Confirm whether the notebook PDF export path handles declarations placed in cells, with a successful PDF export or a documented limitation as the completion criteria.

Written by the indexing model from the issue text.