{"product_id":"9783540197805","title":"Z User Workshop, York 1991: Proceedings of the Sixth Annual Z User Meeting, York 16–17 December 1991","description":"\u003ch1\u003eZ User Workshop, York 1991: Proceedings of the Sixth Annual Z User Meeting, York 16–17 December 1991\u003c\/h1\u003e \u003ch2\u003eNicholls, J. E.\u003c\/h2\u003e \u003cp\u003eIn ordinary mathematics, an equation can be written down which is syntactically correct, but for which no solution exists. For example, consider the equation x = x + 1 defined over the real numbers; there is no value of x which satisfies it. Similarly it is possible to specify objects using the formal specification language Z [3,4], which can not possibly exist. Such specifications are called inconsistent and can arise in a number of ways. Example 1 The following Z specification of a functionf, from integers to integers \"f x : ~ 1 x ~ O· fx = x + 1 (i) \"f x : ~ 1 x ~ O· fx = x + 2 (ii) is inconsistent, because axiom (i) gives f 0 = 1, while axiom (ii) gives f 0 = 2. This contradicts the fact that f was declared as a function, that is, f must have a unique result when applied to an argument. Hence no suchfexists. Furthermore, iff 0 = 1 andfO = 2 then 1 = 2 can be deduced! From 1 = 2 anything can be deduced, thus showing the danger of an inconsistent specification. Note that all examples and proofs start with the word Example or Proof and end with the symbol.1.\u003c\/p\u003e \u003ch3\u003eDetails\u003c\/h3\u003e \u003cp\u003ePublished by: Springer\u003c\/p\u003e \u003cp\u003ePublication Date: 1992-08-06\u003c\/p\u003e \u003cp\u003eFormat: Paperback\u003c\/p\u003e \u003cp\u003eISBN-13: 9783540197805\u003c\/p\u003e \u003cp\u003eDOI: 10.1007\/978-1-4471-3203-5\u003c\/p\u003e \u003cp\u003eDimensions: 242cm x170cm\u003c\/p\u003e \u003cp\u003ePages: 408\u003c\/p\u003e ","brand":"Springer","offers":[{"title":"Default Title","offer_id":44398774452364,"sku":"9783540197805","price":49.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0710\/9545\/1788\/files\/9783540197805.jpg?v=1755443806","url":"https:\/\/fh90cf-fv.myshopify.com\/products\/9783540197805","provider":"Late Knight Books and Services, LLC","version":"1.0","type":"link"}