INTUITIONISTIC LOGIC
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Brouwer's foundational theory ofmathematics which says that you should not count a proof of(There exists x such that P(x)) valid unless the proofactually gives a method of constructing such an x. Similarly,a proof of (A or B) is valid only if it actually exhibitseither a proof of A or a proof of B.In intuitionism, you cannot in general assert the statement (Aor notA) (the principle of the excluded middle); (A ornotA) is not proven unless you have a proof of A or a proofof notA. If A happens to be undecidable in your system(some things certainly will be), then there will be no proofof (A or notA).This is pretty annoying; some kinds of perfectlyhealthylooking examples of proof by contradiction just stopworking. Of course, excluded middle is a theorem ofclassical logic (i.e. nonintuitionistic logic).History(http://britanica.com/bcom/eb/article/3/0,5716,118173+14+109826,00.html).
By Denis Howe
Word of the day
Sexual Arousal Disorders
 Disturbances in desire psychophysiologic changes that characterize the sexual response cycle cause marked distress and interpersonal difficulty. (APA, DSMIV, 1994)