The abbreviation cf. (for Latin confer or conferatur, both meaning 'compare') is generally used in writing to refer the reader to other material to make a comparison with the topic being discussed. Different style guides offer differing advice.
In Italian, the abbreviation "cfr." (confronta, 'confront') is more common than "cf."
Centi (symbol c) is a unit prefix in the metric system denoting a factor of one hundredth. Proposed in 1793, and adopted in 1795, the prefix comes from the Latin centum, meaning "hundred" (cf. century, cent, percent, centennial). Since 1960, the prefix is part of the International System of Units (SI). It is mainly used in combination with the unit metre to form centimetre, a common unit of length.
Chaon (Greek: Χάων, gen.: Χάονος) was a Trojan hero and the eponymous ancestor of the Chaonians in Virgil's Aeneid. The story is unclear as to whether he was the friend or the brother of Helenus, but in either case, he accompanied him to the court of Neoptolemus. Chaon's death is as unclear as that of his relationship to Helenus. Chaon was either killed in a hunting accident or offered himself as a sacrifice to the gods during an epidemic, thus saving the lives of his countrymen. In either case, when Helenus became the ruler of the country, he named a part of the kingdom after Chaon; Chaonia.
The name Χάων 'Chaon' derives from the Greek *χαϝ-ών 'place with abysses'; cf. Χάον ὄρος 'Chaon mountain' in Argolis, χάος 'chaos, space, abyss', χάσκω 'to yawn', χάσμα 'chasm, gorge'. Chaon was also a common Ancient Greek name (Chaon son of Philoumenos - Χάων Φιλουμένου, and Chaon son of Eudoxos - Χάων Εὐδόξου).
In electrostatics, a perfect conductor is an idealized model for real conducting materials. The defining property of a perfect conductor is that static electric field and the charge density both vanish in its interior. If the conductor has excess charge, it accumulates as an infinitesimally thin layer of surface charge. An external electric field is screened from the interior of the material by rearrangement of the surface charge.
Alternatively, a perfect conductor is an idealized material exhibiting infinite electrical conductivity or, equivalently, zero resistivity (cf. perfect dielectric). While perfect electrical conductors do not exist in nature, the concept is a useful model when electrical resistance is negligible compared to other effects. One example is ideal magnetohydrodynamics, the study of perfectly conductive fluids. Another example is electrical circuit diagrams, which carry the implicit assumption that the wires connecting the components have no resistance. Yet another example is in computational electromagnetics, where perfect conductors can be simulated faster, since the parts of equations that take finite conductivity into account can be neglected.