​Janusz Brzdek has published numerous papers on Ulam type stability (e.g., of functional, difference, differential and integral equations), its applications and connections to other areas of mathematics. He has been editor of several books and special volumes focused on such subjects. He was the chairman of the organizing and/or scientific committees of several conferences on Ulam type stability and on functional equations and inequalities.Dorian Popa is the author of numerous papers on Ulam type stability of functional equations, differential equations, linear differential operators, and positive linear operators in approximation theory. Other papers deal with the connections of Ulam type stability with some topics of multivalued analysis (e.g., the existence of a selection of a multivalued operator satisfying a functional inclusion associated to a functional equation).Themistocles M. Rassias published more than 300 papers, 10 research books and 45 edited volumes in research Mathematics as well as 4 textbooks in Mathematics (in Greek) for university students. His research work has received more than 15,000 citations according to Google Scholar and more than 4,900 citations according to MathSciNet. His h-index is 44. He serves as a member of the Editorial Board of several international mathematical journals. His publications have strongly influenced the development of the theory of Ulam stability.

• Survey on Cauchy functional equation in lattice environments.- A purely fixed point approach to the Ulam-Hyers stability and hyperstability of a general functional equation.- Birkhoff–James orthogonality reversing property and its stability.- Optimal forward contract design for inventory: a value-of-waiting analysis.- Ulam-Hyers stability of functional equations in quasi-b-Banach spaces.- On stability of the functional equation of p-Wright affine functions in 2-Banach spaces.- On solutions and stability of a functional equation arising from a queueing system.- Approximation by cubic mappings.- Solutions and stability of some functional equations on semigroups.- Bi-additive s-functional inequalities and quasi multipliers on Banach-algebras.- On Ulam stability of a generalization of the Fréchet functional equation on a restricted domain.- Miscellanea about the stability of functional equations.- Subdominant eigenvalue location and the robustness of Dividend Policy Irrelevance.- A fixed point theorem in uniformizable spaces.- Symmetry of Birkhoff-James orthogonality of bounded linear operators.- Ulam stability of zero point equations.- Cauchy difference operator in some Orlicz spaces.- Semi-inner products and parapreseminorms on groups and a generalization of a theorem of Maksa and Volkmann on additive functions.- Invariant means in stability theory.- On geometry of Banach function modules - selected topics.- On exact and approximate orthogonalities based on norm derivatives.

​Janusz Brzdek has published numerous papers on Ulam type stability (e.g., of functional, difference, differential and integral equations), its applications and connections to other areas of mathematics. He has been editor of several books and special volumes focused on such subjects. He was the chairman of the organizing and/or scientific committees of several conferences on Ulam type stability and on functional equations and inequalities.Dorian Popa is the author of numerous papers on Ulam type stability of functional equations, differential equations, linear differential operators, and positive linear operators in approximation theory. Other papers deal with the connections of Ulam type stability with some topics of multivalued analysis (e.g., the existence of a selection of a multivalued operator satisfying a functional inclusion associated to a functional equation).Themistocles M. Rassias published more than 300 papers, 10 research books and 45 edited volumes in research Mathematics as well as 4 textbooks in Mathematics (in Greek) for university students. His research work has received more than 15,000 citations according to Google Scholar and more than 4,900 citations according to MathSciNet. His h-index is 44. He serves as a member of the Editorial Board of several international mathematical journals. His publications have strongly influenced the development of the theory of Ulam stability.

• Survey on Cauchy functional equation in lattice environments.- A purely fixed point approach to the Ulam-Hyers stability and hyperstability of a general functional equation.- Birkhoff–James orthogonality reversing property and its stability.- Optimal forward contract design for inventory: a value-of-waiting analysis.- Ulam-Hyers stability of functional equations in quasi-b-Banach spaces.- On stability of the functional equation of p-Wright affine functions in 2-Banach spaces.- On solutions and stability of a functional equation arising from a queueing system.- Approximation by cubic mappings.- Solutions and stability of some functional equations on semigroups.- Bi-additive s-functional inequalities and quasi multipliers on Banach-algebras.- On Ulam stability of a generalization of the Fréchet functional equation on a restricted domain.- Miscellanea about the stability of functional equations.- Subdominant eigenvalue location and the robustness of Dividend Policy Irrelevance.- A fixed point theorem in uniformizable spaces.- Symmetry of Birkhoff-James orthogonality of bounded linear operators.- Ulam stability of zero point equations.- Cauchy difference operator in some Orlicz spaces.- Semi-inner products and parapreseminorms on groups and a generalization of a theorem of Maksa and Volkmann on additive functions.- Invariant means in stability theory.- On geometry of Banach function modules - selected topics.- On exact and approximate orthogonalities based on norm derivatives.

​Janusz Brzdek has published numerous papers on Ulam type stability (e.g., of functional, difference, differential and integral equations), its applications and connections to other areas of mathematics. He has been editor of several books and special volumes focused on such subjects. He was the chairman of the organizing and/or scientific committees of several conferences on Ulam type stability and on functional equations and inequalities.Dorian Popa is the author of numerous papers on Ulam type stability of functional equations, differential equations, linear differential operators, and positive linear operators in approximation theory. Other papers deal with the connections of Ulam type stability with some topics of multivalued analysis (e.g., the existence of a selection of a multivalued operator satisfying a functional inclusion associated to a functional equation).Themistocles M. Rassias published more than 300 papers, 10 research books and 45 edited volumes in research Mathematics as well as 4 textbooks in Mathematics (in Greek) for university students. His research work has received more than 15,000 citations according to Google Scholar and more than 4,900 citations according to MathSciNet. His h-index is 44. He serves as a member of the Editorial Board of several international mathematical journals. His publications have strongly influenced the development of the theory of Ulam stability.

• Survey on Cauchy functional equation in lattice environments.- A purely fixed point approach to the Ulam-Hyers stability and hyperstability of a general functional equation.- Birkhoff–James orthogonality reversing property and its stability.- Optimal forward contract design for inventory: a value-of-waiting analysis.- Ulam-Hyers stability of functional equations in quasi-b-Banach spaces.- On stability of the functional equation of p-Wright affine functions in 2-Banach spaces.- On solutions and stability of a functional equation arising from a queueing system.- Approximation by cubic mappings.- Solutions and stability of some functional equations on semigroups.- Bi-additive s-functional inequalities and quasi multipliers on Banach-algebras.- On Ulam stability of a generalization of the Fréchet functional equation on a restricted domain.- Miscellanea about the stability of functional equations.- Subdominant eigenvalue location and the robustness of Dividend Policy Irrelevance.- A fixed point theorem in uniformizable spaces.- Symmetry of Birkhoff-James orthogonality of bounded linear operators.- Ulam stability of zero point equations.- Cauchy difference operator in some Orlicz spaces.- Semi-inner products and parapreseminorms on groups and a generalization of a theorem of Maksa and Volkmann on additive functions.- Invariant means in stability theory.- On geometry of Banach function modules - selected topics.- On exact and approximate orthogonalities based on norm derivatives.