Denys Fisher Denys Fisher Denys Fisher (11 May 1918 – 17 September 2002) was an English engineer who invented the spirograph toy and created the company Denys Fisher Toys. He left Leeds University to join the family firm, Kingfisher (Lubrication) Ltd. In 1960 he left the firm to set up his own company, Denys Fisher Engineering, in Leeds. In 1961 the company won a contract with NATO to supply springs and precision components for its 20 mm cannon. Between 1962 and 1964 he developed various drawing machines from Meccano pieces, eventually producing a prototype Spirograph. Patented in 16 countries, it went on
Cone of curves extremal rays of the cone cannot accumulate. If in addition the variety formula_1 is defined over a field of characteristic 0, we have the following assertion, sometimes referred to as the Contraction Theorem: 3. Let formula_48 be an extremal face of the cone of curves on which formula_33 is negative. Then there is a unique morphism formula_50 to a projective variety "Z", such that formula_51 and an irreducible curve formula_8 in formula_1 is mapped to a point by formula_54 if and only if formula_55. (See also: contraction morphism). Cone of curves In mathematics, the cone of curves (sometimes the Kleiman-Mori