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On the superstability of the cosine and sine type functional equations

Fouad LehlouMohammed MoussaAhmed RoukbiSamir Kabbaj — 2016

Annales Universitatis Paedagogicae Cracoviensis. Studia Mathematica

In this paper, we study the superstablity problem of the cosine and sine type functional equations: f(xσ(y)a)+f(xya)=2f(x)f(y) f ( x σ ( y ) a ) + f ( x y a ) = 2 f ( x ) f ( y ) and f(xσ(y)a)−f(xya)=2f(x)f(y), f ( x σ ( y ) a ) - f ( x y a ) = 2 f ( x ) f ( y ) , where f : S → ℂ is a complex valued function; S is a semigroup; σ is an involution of S and a is a fixed element in the center of S.

On the class of order Dunford-Pettis operators

Khalid BourasAbdelmonaim El KaddouriJawad H'michaneMohammed Moussa — 2013

Mathematica Bohemica

We characterize Banach lattices E and F on which the adjoint of each operator from E into F which is order Dunford-Pettis and weak Dunford-Pettis, is Dunford-Pettis. More precisely, we show that if E and F are two Banach lattices then each order Dunford-Pettis and weak Dunford-Pettis operator T from E into F has an adjoint Dunford-Pettis operator T ' from F ' into E ' if, and only if, the norm of E ' is order continuous or F ' has the Schur property. As a consequence we show that, if E and F are two Banach...

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