[Tex/LaTex] How to add \begin{definition} … \end{definition}

Question

I have the following preamble:

\documentclass{article}
\usepackage{graphicx}
\usepackage{hyperref}
\usepackage{amssymb}
\usepackage{amsthm}
\usepackage{yfonts}
\usepackage[inline]{enumitem}

\newcommand{\subscript}[2]{$#1 _ #2$}

\newtheorem{theorem}{Theorem}

\title{Jumbo}



\author{Frode Alfson Bj\o{}rdal}
\date{}




\begin{document}

How can I get \begin{definition} … \end {definition} here?

Answer 1

Just define it using \newtheorem like you have done for environment theorem:

\documentclass{article}
\usepackage{amsthm}
\newtheorem{definition}{Definition}
\begin{document}
\begin{definition}
  This is a definition.
\end{definition}
\end{document}

See also: How do you number theorems but not definitions?.

For more information about \newtheorem and how to use another style for the new theorem environment definition, e.g., using \theoremstyle{definition} before \newtheorem, see the manual of package amsthm.