Blackboard bold is a typeface style, used for certain symbols in mathematical texts, in which certain lines of the symbol are doubled. The symbols denote number sets. One way of producing blackboard bold is to double-strike a character with a small offset on a typewriter, thus they are referred to as double struck. In typography, such a font with characters that are not solid is called an "inline", "shaded" or "tooled" font. In some texts these symbols are shown in bold type. Blackboard bold in fact originated from the attempt to write bold letters on blackboards in a way that differentiated them from non-bold letters i.e. by using the edge rather than point of the chalk. It made its way back into print form as a separate style from ordinary bold starting with the original 1965 edition of Gunning and Rossi's textbook on complex analysis. In the 1960s and 1970s, blackboard bold spread in classrooms. In textbooks, the situation is not so clear cut: many mathematicians adopted blackboard bold, while many others still prefer to use bold.

Well-known books that use blackboard bold style include Lindsay Childs's "A Concrete Introduction to Higher Algebra,", used as a text for undergraduate courses in the U. S. John Stillwell's "Elements of Number Theory," and Edward Barbeau's "University of Toronto Mathematics Competition,", used to prepare for mathematics competitions. Jean-Pierre Serre uses double-struck letters when writing bold on the blackboard, whereas his published works use ordinary bold for the same symbols. Donald Knuth prefers boldface to blackboard bold, did not include blackboard bold in the Computer Modern fonts that he created for the TeX mathematical typesetting system. On the other hand, Serge Lang does use blackboard bold in his famous "Algebra,", used as a text for graduate courses in the U. S. for at least two decades. The Chicago Manual of Style evolved over this issue. In 1993, it advised: "blackboard bold should be confined to the classroom". Whereas in 2003, it stated that "open-faced symbols are reserved for familiar systems of numbers".

TeX, the standard typesetting system for mathematical texts, does not contain direct support for blackboard bold symbols, but the add-on AMS Fonts package by the American Mathematical Society provides this facility. The amssymb package loads amsfonts. In Unicode, a few of the more common blackboard bold characters are encoded in the Basic Multilingual Plane in the Letterlike Symbols area, named DOUBLE-STRUCK CAPITAL C etc; the rest, are encoded outside the BMP, in Mathematical Alphanumeric Symbols from U+1D538 to U+1D550, U+1D552 to U+1D56B and U+1D7D8 to U+1D7E1. The following table shows all available Unicode blackboard bold characters; the symbols are nearly universal in their interpretation, unlike their normally-typeset counterparts, which are used for many different purposes. The first column shows the letter as rendered by the ubiquitous LaTeX markup system; the second column shows the Unicode code point. The third column shows the symbol itself; the fourth column describes known typical usage in mathematical texts.

In addition, a blackboard-bold μn is sometimes used by number theorists and algebraic geometers to designate the group of nth roots of unity. Mathematical alphanumeric symbols Set notation Weisstein, Eric W. "Doublestruck". MathWorld

James Francis Stephens was an English entomologist and naturalist. He is known for the Manual of British Beetles. Stephens was studied at Christ's Hospital, his father was a navy captain his mother was Mary Peck. He went to school at the Blue Coat School, Hertford and at Christ's Hospital, London, he was sent to study under Shute Barrington, the bishop of Durham in 1800. He left in 1807 and worked as a clerk in the Admiralty office, Somerset House, from 1807 to 1845 thanks to his uncle Admiral Stephens. Stephens took an interest in natural history as a schoolboy, he wrote a manuscript Catalogue of British Animals in 1808. He was elected fellow of the Linnean Society on 17 February 1815, of the Zoological Society of London in 1826. From 1815 to 1825 he took a great interest in ornithology and contributed to the work of George Shaw, he was granted leave from office to assist William Elford Leach in 1818 to arrange the insect collection at the British Museum. He returned to the Admiralty but troubles with his superiors led him to retire early leading to loss of part of his pension.

He worked unpaid in the British Museum until his death and described as many as 2800 British insect species. He used a pocket lens rather than a microscope and used a killing bottle with crushed laurel leaves rather than pinning specimens directly as was the practice then. In 1833, he was a founder of. Stephens made a large insect collection. In 1822 he married daughter of a Captain Roberts, their children died young. Stephens was survived by his wife. After his death his insect collection was purchased by the British Museum, his library was bought by Henry Tibbats Stainton who continued to keep Stephen's tradition of keeping the books available to other entomologists on Wednesday evenings. Stainton published a catalogue of these books Bibliotheca Stephensiana. Stephens was the author of General zoology, or Systematic natural history London, Printed for G. Kearsley in part with George Shaw and sole author of the last 6 volumes of the 16 volumes after the death of George Shaw - I-II Mammalia, III- Amphibia, Pisces, VI Insecta, VII-VIII Aves (1809–120, IX-XIV, pt. 1.

Aves, XIV, pt. 2 General index to the zoology by G. Shaw and J. F. Stephens Nomenclature of British Insects: Being a Compendious List of Such Species. A systematic Catalogue of British insects: being an attempt to arrange all the hitherto discovered indigenous insects in accordance with their natural affinities. Containing the references to every English writer on entomology, to the principal foreign authors. With all the published British genera to the present time. Illustrations of British Entomology. In ten volumes.. This work, following an older system of classification, consists of 7 volumes of Mandibulata, 4 volumes of Haustellata, 1 supplementary volume; the plates are coloured by hand, after drawings by C. M. Curtis and John Obadiah Westwood Stephens reported that James Rennie pirated his illustrations in his 1832 Conspectus of the Butterflies and Moths Found in Britain and went to court, he however lost and most of his earnings from his book were lost to legal fees. Stephen's Illustrations of British Entomology entitled British Entomology was in immediate competition with John Curtis' British Entomology.

This gave rise to an acrimonious dispute which split the British entomological establishment into opposing factions for over thirty years. They were never reconciled despite Stephen's close friend John Obadiah Westwood's attempt to heal the rift. While at the University of Cambridge, the student Charles Darwin became an enthusiastic insect collector, he sent Stephens records of the rarer insects he had captured, was delighted when Illustrations of British entomology gave him credit for capturing insects described in 33 entries, quoting his words in all but two of the cases. Darwin recalled in his autobiography "No poet felt more delight at seeing his first poem published than I did at seeing in Stephen's Illustrations of British Insects the magic words,'captured by C. Darwin, Esq.' ", though the closest wording as published appeared differently, as "captured by the Rev. F. W. Hope and C. Darwin, Esq. in North Wales" and "Taken in North Wales by C. Darwin, Esq.". BHL Illustrations of British Entomology BHL A systematic Catalogue of British insects BHL General Zoology

Josef Holeček was a Czechoslovakian sprint canoeist who competed in the late 1940s and early 1950s. Competing in two Summer Olympics, he won gold medals in the C-1 1000 m event in both 1948 and 1952. Holeček won won two medals at the 1950 ICF Canoe Sprint World Championships in Copenhagen with a gold in the C-1 1000 m and a silver in the C-1 10000 m events. DatabaseOlympics.com profile at the Wayback Machine ICF medalists for Olympic and World Championships – Part 1: flatwater: 1936–2007 at WebCite. Additional archives: Wayback Machine. ICF medalists for Olympic and World Championships – Part 2: rest of flatwater and remaining canoeing disciplines: 1936–2007 at WebCite Evans, Hilary. "Josef Holeček". Olympics at Sports-Reference.com. Sports Reference LLC