In this paper, we prove the Hyers-Ulam stability of the functional equation f(x + y, z + w) + f(x + σ (y), z + τ(w)) = 2f(x, z) + 2f(y, w), where σ, τ are involutions.
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Let R be a 2-torsion free semiprime ring equipped with an involution *. An additive mapping T : R → R is called a left (resp. right) Jordan α-* centralizer associated with a function α : R → R if T(x2) = T(x)α(x*) (resp. T(x2) = α(x*)T(x)) holds for all x (…) R. If T is both left and right Jordan α-* centralizer of R, then it is called Jordan α-* centralizer of R. In the present paper it is shown that if α is an automorphism of R, and T : R → R is an additive mapping such that 2T(xyx) = T(x)α(y*x*) + α(x*y*)T(x) holds for all x; y (…) R, then T is a Jordan α-* centralizer of R.
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Quantifiers on lattices with an antitone involution are considered and it is proved that the poset of existential quantifiers is antiisomorphic to the poset of relatively complete sublattices.
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Pupils of secondary school as well as students often have problems with calculating the sums of the mth powers of successive natural numbers. In this paper we present certain methods of finding such sums.
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E. Pannwitz showed in 1952 that for any n≥2, there exist continuous maps φ : Sn → Sn and f : Sn → R2 such that f(x) ≠ f(φ(x)) for any x ∈ Sn. We prove that, under certain conditions, given continuous maps ψ,φ : X → X and f : X → R2, although the existence of a point x ∈ X such that f(ψ(x)) = f(φ(x)) cannot always be assured, it is possible to establish an interesting relation between the points f(φψ(x)), f(φ2(x)) and f(ψ2(x)) when f(φ(x)) ≠ f(ψ(x)) for any x ∈ X, and a non-standard version of the Borsuk–Ulam theorem is obtained.
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