Extending and paralleling Stechkin's category theorem

We strengthen one of Stechkin's theorems. We also obtain results in the same spirit regarding the farthest point mapping. We work in length spaces, sometimes without bifurcating geodesics, sometimes with geodesic extendability.

On the pillars of Functional Analysis

Many authors consider that the main pillars of Functional Analysis are the Hahn–Banach Theorem, the Uniform Boundedness Principle and the Open Mapping Principle. The first one is derived from Zorn’s Lemma, while the latter two usually are obtained from Baire’s Category Theorem. In this paper we show that these three pillars should be either just two or at least eight, since the Uniform Boundedness Principle, the Open Mapping Principle and another five theorems are equivalent, as we show in a very elemental way. Since one can give an almost trivial proof of the Uniform Boundedness Principle that does not require the Baire’s theorem, we conclude that this is also the case for the other equivalent theorems that, in this way, are simultaneously proved in a simple, brief and concise way that sheds light on their nature.

Some remarks on fuzzy k-pseudometric spaces

An important class of spaces was introduced by I.A. Bakhtin (under the name ?metric-type?) and independently rediscovered by S. Czerwik (under the name ?b-metric?). Metric-type spaces generalize ?classic? metric spaces by replacing the triangularity axiom with a more general axiom d(x,z)? k? (d(x,y)+ d(y,z)) for all x,y,z ? X where k ? 1 is a fixed constant. Recently R. Saadadi has introduced the fuzzy version of ?metric-type? spaces. In this paper we consider topological and sequential properties of such spaces, illustrate them by several examples and prove a certain version of the Baire Category Theorem.

Applications of Baire’s category theorem in complex analysis in one and several complex variables

Στη συγκεκριμένη διατριβή εξετάζουμε μερικές εφαρμογές του θεωρήματος Baire στη Μιγαδική ανάλυση, τόσο στη μία όσο και σε πολλές μιγαδικές μεταβλητές. Τα αποτελέσματα μας σχετίζονται με την έννοια της υπερκυκλικότητας, των πουθενά παραγωγίσιμων (μιγαδικών) συναρτήσεων, των προσεγγιστών Pade, όπως επίσης και με τις καθολικές σειρές Laurent.