\babel@toc {english}{} \contentsline {section}{\numberline {1}Introduction}{3}{section.1}% \contentsline {section}{\numberline {2}Perturbation theory}{3}{section.2}% \contentsline {section}{\numberline {3}Historical overview}{5}{section.3}% \contentsline {subsection}{\numberline {3.1}Behavior of the M{\o }ller-Plesset series}{5}{subsection.3.1}% \contentsline {subsection}{\numberline {3.2}The singularity structure}{6}{subsection.3.2}% \contentsline {section}{\numberline {4}The spherium model}{7}{section.4}%