A transport port is a numbered identifier used by a transport protocol to distinguish communication endpoints at a host. TCP and UDP have separate port spaces.

Data retransmission sends data again to recover from loss or detected corruption. Transport sequence numbers let a receiver recognize a duplicate if the original transmission arrived but its acknowledgement was lost.

A transport sequence number identifies a data position within an exchange, supporting ordering, duplicate rejection and precise acknowledgements. TCP numbers bytes rather than simply numbering packets.

An acknowledgement reports receipt according to the protocol's rules. A TCP cumulative acknowledgement names the next expected byte; it does not establish that the application has durably acted on all preceding data.

A sliding window protocol permits a range of numbered data to be outstanding or accepted, advancing that range as transmission makes progress.

Flow control limits a sender according to a receiver's buffering or processing capacity, rather than the capacity of the intervening computer network.

Scala orders a class and its inherited traits to resolve member lookup and super calls. For two independent traits sharing a base, the rightmost mixed-in trait comes first, followed by the earlier trait and then the common base. Ordinary virtual calls start at the receiver's most specific override; an unqualified super call starts after the implementation's owner in that receiver's linearization. It does not necessarily call the textual parent of the trait in isolation.^[ref]

A Hausdorff compactification is a compact Hausdorff space $K$ with a topological embedding $j:X\to K$ whose image is dense. It retains the original topology on $X$ while adjoining boundary points. For a locally compact noncompact Hausdorff space, its one-point compactification is an example. For every Tychonoff space, the Stone-Čech compactification extends all continuous maps into compact Hausdorff targets.

A space is zero-dimensional when its topology has a base of clopen sets. In the Hausdorff setting these sets separate distinct points, so the space is totally disconnected. Conversely a compact Hausdorff totally disconnected space has a clopen base, by the Šura-Bura component lemma and finite subcovers of the complement of a neighborhood.

Fix a point $a$ of an uncountable set $X$ and declare $F$ closed when $a\in F$ or $F$ is countable. Finite unions and arbitrary intersections satisfy the closed-set axioms. Every convergent sequence is eventually constant: the countable set of its values different from the limit is closed, so its complement is a neighborhood of the limit. A real-valued map constant at $f(a)$ outside a countable set is continuous, because each closed inverse image either contains $a$ or lies in that countable exceptional set.

For a family of functions $f_i:X\to Y_i$ into topological spaces, the initial topology on $X$ is the coarsest topology making them all continuous. Its subbasis consists of $f_i^{-1}(U)$ for open subsets $U\subseteq Y_i$. A map into $X$ is continuous exactly when all its composites with the $f_i$ are continuous.

Erectile tissue is vascular tissue whose filling and outflow properties permit a substantial change in volume or stiffness. Its behavior depends on blood flow and smooth-muscle regulation, linking vascular physiology to organ mechanics. It is not simply ordinary muscle that becomes rigid by contracting.

The +2 oxidation state of tin. The actual aqueous species can depend on pH, hydrolysis and ligands; a bare ionic formula is an analytical shorthand.

The +4 oxidation state of tin. The actual aqueous species can depend on pH, hydrolysis and ligands; a bare ionic formula is an analytical shorthand.

A tin oxide whose hydrated forms may precipitate through hydrolysis of suitable tin(IV) solutions.

The yellow sulfide used in qualitative recognition of suitable tin(IV) solutions.

The brown or brown-black sulfide formed from suitable tin(II) solutions.

Coordinate time labels events in a chosen spacetime chart. It is distinct from proper time, which is measured by a clock along its timelike path. For a stationary observer in a static metric with signature $(+---)$, the rate is $d\tau =\sqrt{g_{tt}}dt$ in units with light speed one. Different stationary observers can therefore accumulate different proper times during the same coordinate-time interval.

Hypothyroidism is insufficient thyroid-hormone action resulting from inadequate hormone availability in the usual clinical setting. Dysfunction can arise in the thyroid or in its upstream control. Measuring thyroid-stimulating hormone and thyroid hormones helps distinguish those pathways.^[ref]

A goitre is enlargement of the thyroid. It is an anatomy description that can accompany different states of glandular secretion and different causes. Measuring the gland's size therefore answers a different question from measuring thyroid hormone secretion or its response to thyroid-stimulating hormone.