\documentclass[a4paper, 11pt]{article}
\begin{document}

\section{Introduction}

This document describes the interfaces which are defined in xia2.

\section{DataCollector}

\section{FrameProcessor}

\section{StrategyComputer}

\section{Indexer}

\section{Integrater}

\section{SubstructureFinder}

An interface which presents options for obtaining a substructure.

\section{MolecularReplacer}

Something which does molecular replacement.

\section{PhaseComputer}

An interface (general) for basic phasing requirements. This may use, in 
addition, either substructure determination or molecular replacement.

\section{PhaseImprover}

Something which improves phases, e.g. through density modification.

\section{MRPhaser}

\section{HAPhaser}

\end{document}

