Due to unplanned maintenance of the back-end systems supporting article purchase on Cambridge Core, we have taken the decision to temporarily suspend article purchase for the foreseeable future. We apologise for any inconvenience caused whilst we work with the relevant teams to restore this service.

*Forum of Mathematics, Pi* and *Forum of Mathematics, Sigma* are an exciting development in journal publishing. Together they offer fully open access publication combined with peer-review standards set by an international editorial board of the highest calibre, and all backed by Cambridge University Press and our commitment to quality.

Strong research papers from all parts of pure mathematics and related areas will be welcomed. All published papers will be free online to readers in perpetuity. An article processing charge for authors will be set at a rate justified by real publishing costs.

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##### Forum of Mathematics, Pi

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##### Forum of Mathematics, Sigma

*Forum of Mathematics, Pi* is the open access alternative to the leading generalist mathematics journals and are of real interest to a broad cross-section of all mathematicians. Papers published are of the highest quality.

*Forum of Mathematics, Sigma* is the open access alternative to the leading specialist mathematics journals. Editorial decisions are made by dedicated clusters of editors concentrated in the following areas: foundations of mathematics, discrete mathematics, algebra, number theory, algebraic and complex geometry, differential geometry and geometric analysis, topology, analysis, probability, differential equations, computational mathematics, applied analysis, mathematical physics, and theoretical computer science. This classification exists to aid the peer review process. Contributions which do not neatly fit within these categories are still welcome.