# Added vertical space on first page if starting with an equation [duplicate]

Consider this simple MWE:

\documentclass{article}
\usepackage[a6paper,showframe]{geometry}
\setlength{\parindent}{0pt}
\begin{document}
Hello world
\end{document}


This is all fine. But if I start the document with an equation, then there is some added vertical space. Does anyone know what is causing this? I'm guessing there is some \vskip command in a .cls file where this is being defined?

\documentclass{article}
\usepackage[a6paper,showframe]{geometry}
\usepackage[fleqn]{mathtools}
\setlength{\mathindent}{0pt}
\begin{document}
\begin{equation*}
\text{Hello world}
\end{equation*}
\end{document}


• Probably related: tex.stackexchange.com/questions/36954/… – nox Jul 28 '18 at 9:20
• @nox Thanks, actually I think I've found the answer in tex.stackexchange.com/questions/267972/…. If I insert \noindent, the vertical space goes away. – Milo Jul 28 '18 at 9:27
• Still not entirely sure where this vertical space originates from though. And how is it being defined? – Milo Jul 28 '18 at 9:35
• From my observation, it doesn't make a difference for the positioning of the equation whether you put some text in the first line or skip it and print the equation. Maybe the equation is set in a \vbox that shifts down due to the indentation? – nox Jul 28 '18 at 9:42
• Informally speaking, without \noindent you get an empty line (10pt high), then 10pt of space (from \abovedisplayskip), then the “Hello world” text; with \noindent the first two are omitted. – GuM Jul 28 '18 at 9:51