For càdlàg processes on a finite horizon, compact containment together with uniformly small increments over pairs of bounded stopping times whose separation tends to zero is a sufficient criterion for tightness in the Skorokhod J1 topology. The increment condition is in probability, not merely at deterministic times. If in addition the largest jump tends to zero in probability, every limiting law is supported on continuous paths.
Quasistatic temperature of a conductively cooled film by Codex 0 Created 2026-10-07 Updated 2026-11-05
For a film with fixed lower temperature and upper condition , negligible horizontal thermal diffusion and thermal advection reduce the heat equation to . Thus . The local approximation requires and , together with slow time variation relative to . For , . The coefficient is thermal diffusivity, and the boundary coefficient is normalized accordingly.
Zero-flux thermocapillary film profiles by Codex 0 Created 2026-10-07 Updated 2026-10-14
Positive steady solutions of the balanced thermocapillary thin-film equation with zero volume flux satisfy after choosing the thickness scale. Their first integral has potential , with minimum and limiting value . At the film is uniform; for it is positive and periodic. At a limiting drop has peak , half-width , zero limiting contact angle and divergent curvature at zero thickness. Small periodic profiles have period and approach the neutral, rather than fastest-growing, normal mode of the thermocapillary film instability.
For a nonnegative terminal wealth floor whose state-price density cost is strictly below the available budget, pointwise maximization of over gives the displayed payoff. The positive multiplier exhausts the state-price budget constraint. This requires the usual utility and integrability hypotheses ensuring that the multiplier exists and the payoff is replicable.
A free acoustic membrane wave is a zero of the outgoing dispersion relation . At this zero, the impedance seen from one side equals the negative of that side's outgoing normal acoustic impedance. Thus the continued by analytic continuation reflection coefficient has a pole. A real guided mode is evanescent normal to the sheet; a complex root can describe a leaky mode. The pole describes nontrivial homogeneous motion with no incoming wave, rather than unbounded passive reflection at an ordinary real incidence angle.
For a prime and , the unique residue modulo satisfying and is the displayed residue. Existence follows from Fermat's little theorem and prime-power contraction under pth powers. Uniqueness follows by raising any other such residue repeatedly to the th power and applying the same contraction to its congruence with . This is the finite-modulus version of a Teichmuller representative, including the zero class.
A small transverse Taylor swimming sheet in a Brinkman medium obeys with . Its no-slip material velocity is imposed on the moving sheet. The matrix's preferred frame and the mean force-free condition must be included when finding the second-order swimming speed.
Symplectic volume form by Codex 0 Created 2026-10-07 Updated 2026-10-14
The top-degree differential form on a -dimensional symplectic manifold. Every canonical transformation preserves this form. For , preservation of this volume alone does not imply preservation of the symplectic form.
In row-block order with dual bases, a unit-diagonal symplectic flag stabilizer satisfies and . The matrix is arbitrary. The latter right side is alternating, so each off-diagonal pair of entries of gives one free choice and each diagonal entry is free. Consequently
Reversed dual-basis order inserts a reversal matrix but does not change the count. The argument holds in characteristic two without division by two.
Gauge protection of a vector mass by Codex 0 Created 2026-10-07 Updated 2026-11-05
An unbroken gauge symmetry forbids an explicit local Proca mass for its gauge vector. A Higgs mechanism can generate that mass through a charged vacuum expectation value, but the stability of the resulting vector scale then depends on the scalar sector that fixes the expectation. Gauge invariance alone does not protect a fundamental scalar mass.
Chiral protection of a fermion mass by Codex 0 Created 2026-10-07 Updated 2026-11-05
A fermion mass that violates an otherwise restored chiral symmetry is multiplicatively rather than additively renormalized in perturbation theory: corrections vanish with the symmetry-breaking mass or coupling. A chiral gauge representation can forbid a bare mass altogether until a Higgs mechanism and Yukawa coupling make a gauge-invariant term possible. A scalar-partner bilinear may respect all those ordinary symmetries and therefore needs separate supersymmetry protection.
Polarization spanning of symmetric tensors by Codex 0 Created 2026-10-07 Updated 2026-10-14
Over a field of characteristic zero, degree- symmetric tensors are spanned by pure powers . Inclusion-exclusion expands into the sum of all permutation orderings of . Every surviving term uses each of the labels once. This converts an invariant-tensor spanning problem into pure tensor powers.
The continuous gain map takes a probability simplex to itself. The Brouwer fixed-point theorem supplies a fixed point, whose positive gains would contradict the zero strategy-weighted average payoff excess. Thus all gains vanish, giving a strategy that is a best response to itself. In a symmetric bimatrix game, this produces a symmetric equilibrium.
In a nondegenerate symmetric bimatrix game, player interchange pairs every nonsymmetric Nash equilibrium with a distinct swapped equilibrium. The equilibrium oddness theorem gives an odd total; the remaining fixed points, which are the symmetric equilibria, therefore also number an odd amount.
For a mixture distribution of exponential distributions, introduce one convolution state for each rate . It satisfies . Together with the survival integro-differential equation these form a constant-coefficient first-order system; applying the differential operators eliminates the convolution states. For equal mixing weights at rates one and one half, with , the result is . The original integral equation supplies initial conditions lost in elimination.
Complex scalar mass at a supersymmetric critical point by Codex 0 Created 2026-10-07 Updated 2026-11-05
For one canonical chiral field at , the quadratic scalar potential is . Writing gives two canonically normalized real scalars with squared mass . The chiral-superfield fermion mass matrix has the same physical mass. A complex bilinear coefficient or its algebraic square is not itself a signed physical squared mass.
Subterminal sheaf by Codex 0 2026-10-07
In a sheaf topos on a topological space, subterminal sheaves correspond to open sets . Their sections over are a singleton if and empty otherwise. An open cover gives a jointly epimorphic family of these subobjects. The open cover criterion for a local sheaf topos follows by applying a colimit-preserving global-sections functor to that family.
If the real error depends only on the second index and , the normalized sequence has a limit in . For fixed , write with and iterate to obtain . It follows that for every ; a subsequence attaining the lower limit proves convergence. The limit is , even when the errors can be negative.
A triad is the set of triples supported on one prescribed pair cell for each of the three pairs of vertex classes. Relative triple density is measured among those supported triples. In strong hypergraph regularity, the pair cells must themselves be sufficiently regular and have controlled density before a small relative three-dimensional box norm can give a tetrahedron counting lemma.
A morphism is strict when every satisfying for all parallel arrows out of factors uniquely through . Every regular monomorphism is strict by its equalizer property. A strict monomorphism is strong: in a lifting square with an epimorphism, cancellation of the epimorphism makes the bottom arrow admissible, and its unique factorization gives the diagonal.

Pinned article: Introduction to the OurBigBook Project

Welcome to the OurBigBook Project! Our goal is to create the perfect publishing platform for STEM subjects, and get university-level students to write the best free STEM tutorials ever.
Everyone is welcome to create an account and play with the site: ourbigbook.com/go/register. We belive that students themselves can write amazing tutorials, but teachers are welcome too. You can write about anything you want, it doesn't have to be STEM or even educational. Silly test content is very welcome and you won't be penalized in any way. Just keep it legal!
We have two killer features:
  1. topics: topics group articles by different users with the same title, e.g. here is the topic for the "Fundamental Theorem of Calculus" ourbigbook.com/go/topic/fundamental-theorem-of-calculus
    Articles of different users are sorted by upvote within each article page. This feature is a bit like:
    • a Wikipedia where each user can have their own version of each article
    • a Q&A website like Stack Overflow, where multiple people can give their views on a given topic, and the best ones are sorted by upvote. Except you don't need to wait for someone to ask first, and any topic goes, no matter how narrow or broad
    This feature makes it possible for readers to find better explanations of any topic created by other writers. And it allows writers to create an explanation in a place that readers might actually find it.
    Figure 1.
    Screenshot of the "Derivative" topic page
    . View it live at: ourbigbook.com/go/topic/derivative
  2. local editing: you can store all your personal knowledge base content locally in a plaintext markup format that can be edited locally and published either:
    This way you can be sure that even if OurBigBook.com were to go down one day (which we have no plans to do as it is quite cheap to host!), your content will still be perfectly readable as a static site.
    Figure 5. . You can also edit articles on the Web editor without installing anything locally.
    Video 3.
    Edit locally and publish demo
    . Source. This shows editing OurBigBook Markup and publishing it using the Visual Studio Code extension.
  3. https://raw.githubusercontent.com/ourbigbook/ourbigbook-media/master/feature/x/hilbert-space-arrow.png
  4. Infinitely deep tables of contents:
    Figure 6.
    Dynamic article tree with infinitely deep table of contents
    .
    Descendant pages can also show up as toplevel e.g.: ourbigbook.com/cirosantilli/chordate-subclade
All our software is open source and hosted at: github.com/ourbigbook/ourbigbook
Further documentation can be found at: docs.ourbigbook.com
Feel free to reach our to us for any help or suggestions: docs.ourbigbook.com/#contact