Q: Custom theorem numbering ... and extend to lemma etc In Custom theorem numbering @egreg provided a way to custome theorem numbering:
\documentclass{article}
%\usepackage{amsthm} %% uncomment to see the difference
\newtheorem{innercustomthm}{Theorem}
\newenvironment{customthm}[1]
  {\renewcommand\theinnercustomthm{#1}\innercustomthm}
  {\endinnercustomthm}

\begin{document}

\begin{customthm}{8}[Somebody]\label{eight}
Every theorem must be numbered by hand.
\end{customthm}

Here is a reference to theorem~\ref{eight}.
\end{document}

Now I tend to extend such approach to Lemma, Definition, Corollary etc. However I got an error extending to Lemma.
I put in
\newtheorem{innercustomlemma}{Lemma}
\newenvironment{customlemma}[1] 
  {\renewcommand\theinnercustomlemma{#1}\innercust‌​omlemma} 
  {\endinnercustomlemma}

at the beginning then 
\begin{customlemma}{abc}[abcd]\label{abcde} 
  abcdef 
\end{customthm}

at the body. The error says: 
! Undefined control sequence. \customlemma ...heinnercustomlemma {#1}\innercust 
                                                                                omlemma 
l.126 \begin{customlemma}{abc} 
                                 [abcd]\label{abcde} ? 

I wonder what shall I do?
Also, the font inside theorem is italic by default, I wonder if this could be tuned off?
