I am using theorem, lemma,corollary, and proof environments with the following way.


All of them properly works excluding the proof. When I start a proof with


here is what I see. If I use \usepackage{amsthm} to use proof, then it messes up the other environments and this is what I get.

I am using the LaTeX INFORMS Journal on Computing Style Files template provided in this website. Then, I open the template and add the \newtheoremcommands as shown above. If I put the following code block and compile, I receive the error.

Here is my theorem.
This is the lemma.
this is the proof.
  • Please post a compilable code reproducing the problem. It is impossible to give an answer/help with only these elements.
    – Bernard
    Dec 17 '19 at 18:17
  • @Bernard I added some extra information. I believe that it is related to the template that I am using.
    – whitepanda
    Dec 17 '19 at 18:24
  • 1
    amsthm provides a proof so you don't need to define it.
    – Sigur
    Dec 17 '19 at 18:40
  • @Sigur As I mentioned in the original post, when I use amsthm , it creates more problem. Of course, when I use that package, I remove the \newtheorem commands.
    – whitepanda
    Dec 17 '19 at 18:44
  • 1
    Maybe try loading ntheorem, which has a syntax close to theorem and defines a nonumberplain theorem style.
    – Bernard
    Dec 17 '19 at 20:30

The class predefines several theorem-like environments and a proof environment that requires an argument.

%% Author template for INFORMS Journal on Computing (ijoc)
%% Mirko Janc, Ph.D., INFORMS, mirko.janc@informs.org
%% ver. 0.95, December 2010
\documentclass[ijoc,nonblindrev]{informs3} % current default for manuscript submission

\OneAndAHalfSpacedXII % current default line spacing

% If hyperref is used, dvi-to-ps driver of choice must be declared as
%   an additional option to the \documentclass. For example
%\documentclass[dvips,ijoc]{informs3}      % if dvips is used
%\documentclass[dvipsone,ijoc]{informs3}   % if dvipsone is used, etc.

% Private macros here (check that there is no clash with the style)

% Natbib setup for author-year style
 \bibpunct[, ]{(}{)}{,}{a}{}{,}%
 \def\newblock{\ }%

%% Setup of theorem styles. Outcomment only one. 
%% Preferred default is the first option.
\TheoremsNumberedThrough     % Preferred (Theorem 1, Lemma 1, Theorem 2)
%\TheoremsNumberedByChapter  % (Theorem 1.1, Lema 1.1, Theorem 1.2)

%% Setup of the equation numbering system. Outcomment only one.
%% Preferred default is the first option.
\EquationsNumberedThrough    % Default: (1), (2), ...
%\EquationsNumberedBySection % (1.1), (1.2), ...

% In the reviewing and copyediting stage enter the manuscript number.
%\MANUSCRIPTNO{} % When the article is logged in and DOI assigned to it,
                 %   this manuscript number is no longer necessary


All natural numbers are interesting.

Clearly $0$ is interesting. Suppose there is a number that's not interesting
and call $n$ the minimal such. Then it is the minimal uninteresting number,
so obviously it is interesting.


Note that you must add an argument to \begin{proof}.

enter image description here

  • 1
    Thanks, man! It was literally driving me crazy.
    – whitepanda
    Dec 17 '19 at 21:10

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