A test named after Hermann von Fehling. Heating with Fehling's reagent can produce copper(I) oxide from reducing sugars; several different substances can give a positive result.

For a node $v$ of a red-black tree, count black nodes strictly below $v$ on any path to an absent-child sentinel, including that black sentinel. The red-black invariants make this count independent of the path. Other conventions omit the sentinel or count $v$; specify the convention when using numerical values. Equality of the counts, rather than their common additive offset, is what the balancing condition requires.

A red-black tree with no red stored nodes is a perfect binary tree. Indeed, every root-to-sentinel path has equal length because every real node is black; a missing branch at an earlier level would make its path shorter. Thus every real level is full. Its size is $2^h-1$ for some number $h$ of real levels. Conversely, colouring every stored node of a perfect binary tree black satisfies every red-black invariant. This proves both directions of the size criterion.

In the usual bottom-up algorithm, insert a red node by the binary search tree rule. If its parent is black, no repair is needed. If its parent and uncle are red, recolour both black and recolour the grandparent red, then continue upward. If the uncle is black, an inner configuration first rotates the parent to become an outer configuration; rotating the grandparent and exchanging its colour with the parent's resolves the red-red conflict. Apply the left/right mirror cases as needed and finish with a black root. The tree rotations preserve key order, and the colour changes preserve equal black height. Different valid insertion conventions can produce different valid red-black trees, so a worked trace must identify its convention.

A formal language whose complement of a set, relative to the set of all input words, is a recursively enumerable language. A recognizer for the complement detects every negative instance eventually and need not halt on positive instances. A formal language is a decidable language exactly when it and its complement are both recursively enumerable languages.

For a fixed natural number $a$ and a standard encoding of natural numbers, validate the input and compare its encoded value with $a$. This decides $L_a$. A well-ordering argument can prove that an upward-closed set of natural numbers has this form without calculating its least element. A decider may contain that fixed least element in its finite description; its existence does not give a uniform method to discover the least element from another program.

A family of programming closures sharing a semantic environment that binds every name in the family. Each body therefore sees every family member, including those whose definitions occur later in the source.

Let $P$ be a nonzero polynomial of even degree $2m$ over a field of characteristic different from two, satisfying the displayed reciprocal identity. If $P(x)=(x-1{)}^{r}A(x)$ with $A(1)\ne 0$, cancellation gives $A(x)=(-1{)}^r{x}^{2m-r}A(1/x)$. Substitution of $x=1$ forces $r$ even. If $P(x)=(x+1{)}^{s}B(x)$ with $B(-1)\ne 0$, cancellation gives $B(x)=x^{2m-s}B(1/x)$; substitution of $x=-1$ forces $s$ even. Zero multiplicities are included. Pairing nonfixed reciprocal roots alone cannot prove this parity, because $1$ and $-1$ are their own inverses.

An interval sufficient to establish that every reader that might retain a preexisting reference has left its protected read-side region. Completion permits the corresponding old object to undergo memory reclamation.

Sending an already produced result directly to a consumer without waiting for its write to the register file. The bypass must choose the youngest older writer whose value is ready.

A ray-plane intersection followed by an inside-triangle test, conveniently using nonnegative barycentric coordinates. Oriented surfaces may additionally require a front-facing hit through back-face culling.

On a finite ground set $E$, a submodular rank function is a normalised set function $r$ with $r(\varnothing )=0$, a monotone set function, and a submodular set function, such that $r(A\cup \{e\})-r(A)\in \{0,1\}$ for $e\notin A$. Equivalently, require nonnegative integer values, monotonicity, submodularity and $r(\{e\})\le 1$. The diminishing returns characterization of submodularity bounds each marginal by its singleton value. Thus $0\le r(A)\le |A|$.

These functions are precisely the rank functions of matroids. To see the converse direction, define $\mathcal{I}=\{A:r(A)=|A|\}$. It contains the empty set. If $B\subseteq A\in \mathcal{I}$, the unit marginal bounds give $|A|=r(A)\le r(B)+|A\setminus B|$, so $r(B)=|B|$ and heredity holds. For augmentation, suppose $A,B\in \mathcal{I}$ with $|A|<|B|$. If every $e\in B\setminus A$ had zero marginal over $A$, diminishing returns would keep each marginal zero as they are added successively. This would give $r(A\cup B)=r(A)=|A|<|B|=r(B)$, contradicting monotonicity. Some marginal is therefore one, giving an independent augmentation.

Finally any inclusion-maximal $I\subseteq A$ in this independence family has $r(I\cup \{e\})=r(I)$ for every remaining $e\in A\setminus I$. Successively adding them and using diminishing returns shows $r(A)=r(I)=|I|$, so the resulting matroid really has rank $r$. The forward direction is submodularity of matroid rank. These integer increment conditions distinguish matroid ranks from arbitrary real-valued submodular functions.

A random variable whose cumulative distribution function is continuous, equivalently whose probability distribution assigns zero probability to every singleton. In elementary applications, one usually additionally assumes a probability density function; that stronger property means its law is an absolutely continuous probability distribution. A continuous cumulative distribution function alone need not admit a probability density function.

On the symmetric small-$Q/\nu$ branch of radial viscous flow in a wedge, the leading Stokes flow solves $G_0^{(3)}+4G_0^{\prime }=0$, zero wall values and unit integral. HenceFor $\pi /2<\alpha <{\alpha }_c$, where ${\alpha }_c\simeq 2.24670$, this is positive in $|\theta |<\pi -\alpha$ and negative near the walls. The normalization denominator tends to zero at the stated root. At the root the homogeneous angular mode has zero net flux, so it cannot be rescaled to carry a fixed nonzero source flux.

Approaching that angle makes large outward and reverse contributions cancel to leave the prescribed flux. The leading amplitude diverges and the nonlinear inertial correction ceases to be perturbative, however small its coefficient is at fixed angle. This is a failure of a regular expansion, not a proof of infinite speed in the full Navier-Stokes equation. Distinct inner scalings or different steady branches require separate analysis.

The posterior interosseous nerve is the continuation of the deep motor pathway of the radial nerve in the forearm. It supplies many extensor muscles. Loss of these movements can occur without the cutaneous sensory loss expected from a more proximal radial-nerve lesion.

For a nonempty subset $A$ of a topological space $X$, identify all points of $A$ and leave each point of $X\setminus A$ in its own equivalence class. The resulting quotient space is denoted $X/A$. For every subset $K\subseteq X$, its saturation of a subset isThe quotient topology therefore gives a useful test: $q_A(K)$ is a closed set if and only if the displayed saturation of a subset is a closed set of $X$. In particular, every closed set disjoint from $A$ has closed image, even if $A$ is not closed. When $A$ is closed, $q_A$ is a closed map, because both possibilities in the formula are then closed sets for closed $K$.

Identify points of the circle having the same real coordinate, equivalently points related by complex conjugation. The continuous surjection $h(z)=(1+\mathrm{Re}z)/2$ has exactly these equivalence classes as its fibers. It induces a continuous bijection from the quotient space to the closed interval. The quotient space is compact as a continuous image of a compact space, while the closed interval is Hausdorff, so the compact-to-Hausdorff continuous bijection theorem makes the induced map a homeomorphism. The two fixed points of the reflection become the two interval endpoints.

A quotient space of a space carrying the cofinite topology has a topology contained in the cofinite topology on its underlying quotient set. If $q:X\to Y$ is the quotient map and $U$ is a nonempty open subset of $Y$, its preimage has finite complement. Since $q$ is surjective, the complement of $U$ is the image of that finite complement, hence is finite. Equality need not hold: partition $\mathbb{Z}$ into its even and odd integers. Both classes are infinite, so their two-point quotient space has the indiscrete topology, whereas the cofinite topology on a finite set is the discrete topology.

Suppose a group acts by isometries on a metric space $X$, and for points $a,b$ in different orbits one has ${\inf }_{g}d(a,gb)>0$. Then the orbit space with its quotient topology is Hausdorff. Indeed, choose $\epsilon$ less than one third of this positive infimum and saturate the open radius-$\epsilon$ balls about $a$ and $b$ by the action. These saturated sets are open because every acting isometry is a homeomorphism. Their translates cannot meet: their centres stay at least the given positive distance apart. Their disjoint open images in the quotient separate the two orbit points, since the preimage of each image is its saturated set. This applies to the glide reflection $(x,y)\mapsto (x+1,-y)$ on a closed strip: the distance from one point to the translates of another tends to infinity as the integer translation grows, so two distinct orbits have a positive minimum distance.

For a topological space $X$, the displayed relation is an equivalence relation. Give its quotient the quotient topology. Every inverse image under a continuous map from $X$ to a Hausdorff space is a saturation of a subset. Distinct quotient classes can be distinguished by some such map; disjoint open neighborhoods of their images pull back to disjoint saturated open sets, whose quotient images are open. Thus the quotient is Hausdorff. Each continuous map from $X$ to a Hausdorff space factors uniquely through this quotient, and the factor is continuous by the quotient topology. This is its universal reflection property.