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The Barcan formula is: . In English, the schema reads: If every x is necessarily F, then it is necessary that every x is F.It is equivalent to . The Barcan formula has generated some controversy because—in terms of possible world semantics—it implies that all objects which exist in any possible world (accessible to the actual world) exist in the actual world, i.e. that domains cannot grow ...
The haversine formula determines the great-circle distance between two points on a sphere given their longitudes and latitudes. Important in navigation , it is a special case of a more general formula in spherical trigonometry , the law of haversines , that relates the sides and angles of spherical triangles.
The Wayback Machine is a digital archive of the World Wide Web founded by the Internet Archive, an American nonprofit organization based in San Francisco, California. Created in 1996 and launched to the public in 2001, it allows users to go "back in time" to see how websites looked in the past.
Internet Archive's Wayback Machine is the largest and oldest web archive in the world, dating back to 1996. Internet Archive also provide various web archiving services, including Archive-IT, Save Page Now, and domain level contract crawls. The Wayback Machine is the publicly available access service to Internet Archive and partners' collections.
The Wayback Machine is about 80% of the total. Data initially compiled by User:GreenC as of March 2017. Updates and corrections welcome. Archive services.
An equivalent (symbol: officially equiv; [1] unofficially but often Eq [2]) is the amount of a substance that reacts with (or is equivalent to) an arbitrary amount (typically one mole) of another substance in a given chemical reaction. It is an archaic quantity that was used in chemistry and the biological sciences (see Equivalent weight § In ...
For hydrocarbons, the DBE (or IHD) tells us the number of rings and/or extra bonds in a non-saturated structure, which equals the number of hydrogen pairs that are required to make the structure saturated, simply because joining two elements to form a ring or adding one extra bond (e.g., a single bond changed to a double bond) in a structure reduces the need for two H's.
The Wayback Machine is a service which can be used to cite archived copies of web pages used by articles. This is useful if a web page has changed, moved, or disappeared; links to the original content can be retained.