For a fibration over $S^n$, the only possible differential in the homological Serre spectral sequence is $d_n$. Identifying its two nonzero columns with the homology of the fiber gives the Wang homomorphism $\Delta$.

A Serre fibration is a map having the homotopy lifting property with respect to every disc, equivalently every CW complex.

A finite-length semisimple module has a canonical decompositionin which $M_i$ is the sum of all simple submodules isomorphic to a fixed simple module $S_i$. Each $M_i$ is isomorphic to a finite direct sum $S_i^{m_i}$.

The decomposition is intrinsic to the semisimple module: the isomorphism types of its simple submodules determine the summands.

The defocusing power-type wave equation has the conserved nonnegative energy

The Page–Geilker experiment used a quantum random decision to choose a macroscopic source-mass configuration and measured its field with a torsion balance. The observed field followed the configuration in the observed branch rather than the nearly cancelling expectation-value average predicted by the simplest no-collapse semiclassical Einstein equation.

A biproduct $A\oplus B$ is simultaneously a product in a category and a coproduct in a category, with projections $p_i$ and injections $i_i$ satisfying

A self-adjoint operator $A$ is positive definite when $⟨Av,v⟩>0$ for every nonzero vector $v$ in its domain. In finite dimension it is invertible and has positive eigenvalues. In infinite dimension, strict positivity of individual quadratic-form values need not give a bounded inverse; the stronger uniform bound $⟨Av,v⟩\ge c\Vert v{\Vert }^2$ with $c>0$ supplies coercivity.

For maps $\beta :U\to V$ and $\gamma :V\to W$ between finite-dimensional inner product spaces, with $\mathrm{im}\beta =\ker \gamma$, the operator $\beta {\beta }^{\ast }+{\gamma }^{\ast }\gamma$ is positive definite. Its quadratic form is $\Vert {\beta }^{\ast }v{\Vert }^2+\Vert \gamma v{\Vert }^2$, whose zero set is $\mathrm{im}\beta \cap (\mathrm{im}\beta {)}^{\perp }=\{0\}$. This uses the adjoint operator relation $\ker {\beta }^{\ast }=(\mathrm{im}\beta {)}^{\perp }$.

Hawking's area theorem states that the total area of classical future event horizons cannot decrease when the null energy condition and the required global assumptions hold. It is the geometric content of the second law of black-hole mechanics.

A score equation sets the score function equal to zero. Its solutions are stationary points of the log-likelihood, and a negative-definite likelihood Hessian identifies an interior local maximum.

The chordal SLE Loewner trace eventually leaves every bounded subset of the complex upper half-plane. For $0<\kappa <4$, its time-one compact H-hull is a simple slit and does not contain a half-disc. Instead, the boundary approach forces a small SLE Bessel gap estimate shows that every fixed nonzero real point is outside the closure of the full Loewner trace. After mapping out the initial simple slit, the starting point has two distinct real prime end images. A fresh independent SLE avoids approaching either image, so the original future stays a positive distance from its starting point. Scaling invariance of SLE gives ${\inf }_{t\ge T}|\gamma (t)|\stackrel{d}{=}\sqrt{T}{\inf }_{t\ge 1}|\gamma (t)|$, and decreasing-event continuity proves escape from every fixed disc. The separate argument based on a swallowed half-disc at positive time applies in the nonsimple regime $\kappa >4$; it must not be applied to a simple slit. The critical parameters require their own limiting or trace-existence arguments.

The trace of ${\mathrm{SLE}}_{\kappa }$ is simple for $0<\kappa \le 4$, has self-intersections without being space-filling for $4<\kappa <8$, and is space-filling for $\kappa \ge 8$. The thresholds arise from the Boundary-point Bessel flow for SLE and estimates for the Loewner chain near its driving point.

Chordal SLE is defined on any simply connected domain with two marked boundary points by applying a conformal map from the upper half-plane. Its law is independent of the chosen map, up to a deterministic change of parameterization.

An exactly marginal operator has scaling dimension equal to the spacetime dimension and a deformation coupling whose beta function vanishes to all orders. Varying that coupling moves along a family of conformal field theories without introducing a scale.

Let $N$ be uncountable and saturated, and let a formula define an equivalence relation. If every small elementary submodel of $N$ meets every class, then there are only finitely many classes. Otherwise a small elementary submodel $M$ yields the finitely satisfiable type $\{\neg E(x,m):m\in M\}$, contradicting saturation.

A universal homogeneous model realizes every type over a small parameter set. Embed a small model containing a realization into the universal model, then use homogeneity to move the embedded parameters back to the original ones.

A model $N$ of cardinality $\kappa$ is homogeneous when every partial elementary map between subsets of size less than $\kappa$ extends to an automorphism of $N$.

A model $N$ of cardinality $\kappa$ is universal when every model of the same complete theory having cardinality less than $\kappa$ admits an elementary embedding into $N$.

If an aleph-zero-homogeneous model realizes every finite type over the empty set, it is aleph-zero-saturated. Realize the joint empty-set type of the parameters and a desired element, then use homogeneity to move the realized parameter tuple to the given one.

A $\kappa$-saturated model has the one-point extension property for partial elementary maps of size below $\kappa$: transport the type of the new element through the map and realize it by saturation. This is $\kappa$-homogeneity; back-and-forth gives the corresponding automorphisms when cardinalities permit.

A Whitehead double is the satellite formed with the Whitehead pattern, which has winding number zero and whose image on the unknot is an unknot. The Satellite formula for the Alexander polynomial therefore gives $\Delta (t)\doteq 1$ for every untwisted Whitehead double.