|  Foliations of Manifolds | 
In General
  * Idea: A p-dimensional foliation
    of an n-dimensional manifold M is a decomposition of M as a union
    of parallel submanifolds (leaves) of dimension p.
  * Leaves: Each leaf in a foliation is
    an embedded submanifold of dimension p.
  * Result: Every complete 2-manifold can occur
    as the leaf of a foliation of a compact 3-manifold, but not every complete 3-manifold can occur
    as the leaf of a foliation of a 4D one!
  > Related topics:
    see embeddings and immersions;
    extrinsic curvature [and extremal surfaces];
    gauge transformations; Hypersurface;
    metric decomposition.
  > Special cases:
    see 3D manifolds;  FLRW spacetime.
  > Online resources:
    see Wikipedia page.
Foliations of Riemannian Manifolds
  * Singular Riemannian foliation: A singular
    foliation is called a singular Riemannian foliation if every geodesic that is perpendicular
    to one leaf is perpendicular to every leaf it meets; A typical example is the partition of
    a complete Riemannian manifold into orbits of an isometric action.
  @ Singular Riemannian foliation:
    Alexandrino et al DG&A(13) [intro].
Foliations of Lorentzian Manifolds
  > s.a. initial-value formulation of general relativity.
  * Spacelike case: A spacetime foliation
    follows from (but is weaker than) a choice of time or gauge in an initial-value formulation;
    Every foliation gives a curve in the space of Riemannian geometries (+ a lapse function + a
    shift vector); The choice of an appropriate foliation is important in numerical relativity.
  @ Spacelike and timelike foliations of spacetime: in Lau CQG(96)gq/95;
    Walschap JGP(99) [spacelike, properties];
    Harris & Low CQG(01)gq [shape of space];
    Husain et al PRD(02)gq/01  [spherical, spatially flat];
    Bolós GRG(07)gq/05 [stability between foliations].
  @ Special spacelike foliations: Delphenich gq/02 [proper time foliations];
    Sánchez & Senovilla CQG(07)-a0709 [with respect to a static Killing vector, uniqueness].
  @ Lightlike foliations: Bolós MPCPS(05)gq.
  @ Constant mean curvature: Christodoulou & Francaviglia GRG(79) [Einstein spacetimes admitting a Gaussian foliation];
    Andersson et al JGP(97)gq/96 [2+1 globally hyperbolic];
    Rendall HPA(96)gq [conjectures],
    CMP(97)gq/96 [with 2 Killing vector fields],
    gq/96-proc [results];
    Andersson & Iriondo gq/97;
    Isenberg & Rendall CQG(98)gq/97 [counterexamples];
    Gowdy gq/01 [Minkowski and Schwarzschild spacetimes];
    Malec & Ó Murchadha PRD(03)gq,
    gq/03,
    PRD(09)-a0903 [Schwarzschild spacetime];
    Klainerman & Rodnianski a0801 [breakdown];
    Martín-Moruno AIP(12)-a1201 [in our region of spacetime];
    Gerhardt a1902
      [spacetimes asymptotic to open FLRW  spacetimes].
  @ Other types: Berger et al AP(97)gq [T2 isometry];
    Henkel AIP(02)gq/01,
    JMP(02)gq/01,
    JMP(02)gq/01 [with prescribed mean curvature];
    Müller a0904/TAMS [globally hyperbolic manifolds, nice foliations];
    García JMP(13)-a1212 [conformally flat leaves].
  @ And singularities: Alcubierre CQG(03) [focusing singularities and gauge shocks].
Related Topic: Webs
  * Web:
    A family of foliations of a manifold in general positions.
  * Orthogonal web:
    In an n-dimensional manifold with metric, a set of n pairwise
    transversal and orthogonal foliations of connected submanifolds of codimension 1.
  @ Web: Chern BAMS(82) [geometry];
    Zakharevich mp/00 [Veronese webs];
    Grifone & Salem ed-01;
    Fleischhack MN(04)mp/03 [parallel transport],
    CMP(04) [degenerate webs].
  > Online resources:
    see Wikipedia page.
References
  @ General: Reinhart 83;
    Bejancu & Farran 06 [and geometric structures].
  @ 3D manifolds:
    Shields T&A(06) [equivalence classes of foliations];
    Calegari 07.
  @ Manifolds that can / cannot be leaves of foliations:
    Cantwell & Conlon Top(87) [every surface is a leaf];
    Attie & Hurder Top(96) [manifolds that cannot].
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  send feedback and suggestions to bombelli at olemiss.edu – modified 12 feb 2019