Search results for "Proof"
showing 10 items of 187 documents
A Pedagogical Proof of Arrow's Impossibility Theorem
1999
In this note I consider a simple proof of Arrow's Impossibility Theorem (Arrow 1963). I start with the case of three individuals who have preferences on three alternatives. In this special case there are 133=2197 possible combinations of the three individuals' rational preferences. However, by considering the subset of linear preferences, and employing the full strength of the IIA axiom, I reduce the number of cases necessary to completely describe the SWF to a small number, allowing an elementary proof suitable for most undergraduate students. This special case conveys the nature of Arrow's result. It is well known that the restriction to three options is not really limiting (any larger se…
INCIDENCE CONSTRAINTS: A COMBINATORIAL APPROACH
2006
The simplest geometric constraints are incidences between points and lines in the projective plane. This problem is universal, in the sense that all algebraic systems reduce to such geometric constraints. Detecting incidence dependences between these geometric constraints is NP-complete. New methods to prove incidence theorems are proposed, which use strictly no computer algebra but only combinatorial arguments.
Heyting-valued interpretations for Constructive Set Theory
2006
AbstractWe define and investigate Heyting-valued interpretations for Constructive Zermelo–Frankel set theory (CZF). These interpretations provide models for CZF that are analogous to Boolean-valued models for ZF and to Heyting-valued models for IZF. Heyting-valued interpretations are defined here using set-generated frames and formal topologies. As applications of Heyting-valued interpretations, we present a relative consistency result and an independence proof.
A short proof of a theorem of Juhasz
2011
Abstract We give a simple proof of the increasing strengthening of Arhangelʼskii Theorem. Our proof naturally leads to a refinement of this result of Juhasz.
Amount of Nonconstructivity in Finite Automata
2009
When D. Hilbert used nonconstructive methods in his famous paper on invariants (1888), P.Gordan tried to prevent the publication of this paper considering these methods as non-mathematical. L. E. J. Brouwer in the early twentieth century initiated intuitionist movement in mathematics. His slogan was "nonconstructive arguments have no value for mathematics". However, P. Erdos got many exciting results in discrete mathematics by nonconstructive methods. It is widely believed that these results either cannot be proved by constructive methods or the proofs would have been prohibitively complicated. R.Freivalds [7] showed that nonconstructive methods in coding theory are related to the notion of…
Eine Bemerkung zum Normenresthomomorphismus $h : K_{\ast} F/2 \longrightarrow H^{\ast} (F, \mathbb{Z}/2)$
2003
An elementary Galois theoretic proof is given for the fact: An element $b \in \dot{F}$ is a norm from the extension $F (\sqrt{a})$ iff $(a) \cup (b) = 0$ in $H^{2} (F, \mathbb{Z}/2)$. From this it follows easily that h exists. Comments about other proofs and applications to quadratic forms conclude the paper.
Contractivity results in ordered spaces. Applications to relative operator bounds and projections with norm one
2016
This paper provides various “contractivity” results for linear operators of the form I−C where C are positive contractions on real ordered Banach spaces X. If A generates a positive contraction semigroup in Lebesgue spaces Lp(μ), we show (M. Pierre's result) that A(λ−A)−1 is a “contraction on the positive cone”, i.e. A(λ−A)−1x≤x for all x∈L+p(μ)(λ>0), provided that p⩾2. We show also that this result is not true for 1 ⩽ p<2. We give an extension of M. Pierre's result to general ordered Banach spaces X under a suitable uniform monotony assumption on the duality map on the positive cone X+. We deduce from this result that, in such spaces, I−C is a contraction on X+ for any positive projection…
The monadic quantifier alternation hierarchy over grids and pictures
1998
The subject of this paper is the expressive power of monadic second-order logic over two-dimensional grids. We give a new, self-contained game-theoretical proof of the nonexpressibility results of Matz and Thomas. As we show, this implies the strictness of the monadic second-order quantifier alternation hierarchy over grids.
Mappings of finite distortion: a new proof for discreteness and openness
2008
We give a new and elementary proof of the known result: a non-constant mapping of finite distortion f : Ω ⊂ ℝn → ℝn is discrete and open, provided that its distortion function if n = 2 and that for some p > n − 1 if n ≥ 3.
Agri-food Supply Chain Traceability for Fruit and Vegetable Cooperatives Using Blockchain Technology
2019
Blockchain se ha convertido en una tecnología disruptiva que tiene la capacidad de transformar la industria agroalimentaria, puesto que promete resolver muchos problemas relacionados con la falta de confianza en la trazabilidad y el producto que adquieren los consumidores. Sin embargo, las partes implicadas en la cadena de suministro de productos agroalimentarios son numerosas y están físicamente dispersas, lo que dificulta el manejo de datos e información. Como resultado, el proceso de producción no es transparente y la confianza es difícil de construir. Para ser más exitosas en la economía globalizada actual, las cooperativas deben focalizarse en ofrecer mayor transparencia. Este document…