Where does contraction collide?

The generation of force by a muscle as its fibres shorten or resist being stretched: at the molecular level the myosin and actin filaments slide past one another, drawn along by cross-bridges, so the sarcomere shortens while the filaments themselves keep their length. Huxley and Niedergerke's 1954 Structural changes in muscle during contraction reported the interference-microscope observations of living fibres that grounded this sliding-filament account. The referent is a mechanical, force-producing event in living tissue, measured in units of force, and it has nothing to do with a shrinking economy, a shortened word, or a distance-reducing map beyond the shared spelling.[1]

Unit

A muscle's developed force, in newtons or as tension per cross-section

Recovery means

The muscle relaxes as cross-bridges detach and calcium is taken back up, and the developed tension falls toward rest

Measured by

Recorded as force or tension with a myograph or force transducer, and traced to sarcomere shortening under the microscope

A phase of the business cycle in which aggregate economic activity falls, running from a peak down to a trough: output, employment, and income decline together across the economy, and a deep or prolonged contraction is what is usually called a recession or depression. Burns and Mitchell's 1946 Measuring business cycles set out the empirical method for marking these expansions and contractions from the turning points shared across many economic series. The referent is a macroeconomic downturn, dated by falling activity over months or quarters, not a muscle developing tension, a word being shortened, or a map drawing points together.[2]

Unit

A fall in aggregate activity, dated as the phase from a peak to a trough

Recovery means

The trough ends the contraction, and the expansion that follows carries activity back up toward and past the previous peak

Measured by

Dated from turning points in output, employment, income, and sales, as by a business-cycle dating committee

A shortened form in which two words are run together and some sounds or letters are dropped, marked in writing by an apostrophe, as do not is reduced to don't: the reduced element leans on a host word rather than standing on its own. Zwicky and Pullum's 1983 Cliticization versus inflection: English n't argued that the negative contraction is better treated as inflection on the auxiliary than as a phonologically reduced clitic. The referent is a morphological and orthographic reduction of words, described by its form and its host, not a muscle shortening, an economy shrinking, or a mapping that brings points closer.[3]

Unit

A single reduced form standing for two words, as don't stands for do not

Recovery means

Not applicable

Measured by

Identified in speech or text by the reduced form and its apostrophe, and analysed as cliticisation or as inflection

A function on a metric space that moves any two points strictly closer together, so that the distance between their images is at most some fixed fraction of the distance between them, with that fraction below one: iterating such a map drives points toward a single fixed point. Banach's 1922 Sur les opérations dans les ensembles abstraits proved that a contraction on a complete metric space has exactly one fixed point, reached by iterating from any starting point. The referent is a formal property of a function, defined by an inequality on distances, and it shares nothing with a muscle, an economy, or a spoken contraction beyond the word.[4]

Unit

A map on a metric space with a Lipschitz constant below one

Recovery means

Not applicable

Measured by

Verified by exhibiting a constant below one such that every pair of images is at most that fraction of the original distance apart