Output is like this
Source file is like the following. Just go to Overleaf, create an account, create and empty project, and copy the following into it.
\documentclass{article} \title{HW7 for 214} \author{John Doe} \usepackage{mathrsfs, amssymb,amsmath,amsthm,amsfonts, mathtools, tikz-cd, tikz} \def\R{\mathbb R} \def\C{\mathbb C} \def\acal{\mathcal A} \def\gfrak{\mathfrak g} \newtheorem{theo}{Theorem}[section] \newtheorem{lemma}[theo]{Lemma} \newtheorem{problem}[theo]{Problem} \newtheorem{corollary}[theo]{Corollary} \newtheorem{proposition}[theo]{Proposition} \begin{document} \maketitle Let $\R$ be the field of real numbers. \begin{proposition} For any right triangle, we have \[ a^2 + b^2 = c^2 \] \end{proposition} \begin{proof} Let me ask Pythagoras. \end{proof} \begin{problem} Let $G$ be a Lie group, show that $T_e G$ can be equipped with a Lie algebra structure. \end{problem} \begin{proof}[Solution] We did this in class. \end{proof} $\gfrak$ is a common symbol for Lie algebra. \end{document}