Riccardo Plati

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2ranked-venue papers
0as first author
2since 2021 · last 2026
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Theory of computation · 2 · 2 since 2021
YearPublicationVenuePosition
2026 A New Weak Choice Principle
abstract
Abstract For every natural number n we introduce a new weak choice principle n upper R upper C Subscript f i n $\mathrm {nRC_{fin}}$ n R C f i n : Given any infinite set x , there is an infinite subset y subset of or equal to x $y\subseteq x$ y ⊆ x and a selection function f that chooses an n-element subset from every finite z subset of or equal to y $z\subseteq y$ z ⊆ y containing at least n elements. By constructing new permutation models built on a set of atoms obtained as Fraïssé limits, we will study the relation of n upper R upper C Subscript f i n $\mathrm {nRC_{fin}}$ n R C f i n to the weak choice principles upper R upper C Subscript m $\mathrm {RC_m}$ R C m (that has already been studied in [3] and [6]): Given any infinite set x , there is an infinite subset y subset of or equal to x $y\subseteq x$ y ⊆ x with a choice function f on the family of all m-element subsets of y . Moreover, we prove a stronger analogue of the results in [6] when we study the relation between
Lorenz Halbeisen, Riccardo Plati, Salome Schumacher
J. Symb. Log.2
2023 Four cardinals and their relations in ZF
abstract
For a set $M$, $\operatorname{fin}(M)$ denotes the set of all finite subsets of $M$, $M^2$ denotes the Cartesian product $M\times M$, $[M]^2$ denotes the set of all $2$-element subsets of $M$, and $\operatorname{seq}^{1-1}(M)$ denotes the set of all finite sequences without repetition which can be formed with elements of $M$. Furthermore, for a set $S$, let $|S|$ denote the cardinality of $S$. Under the assumption that the four cardinalities $|[M]^2|$, $|M^2|$, $|\operatorname{fin}(M)|$, $|\operatorname{seq}^{1-1}(M)|$ are pairwise distinct and pairwise comparable in ZF, there are six possible linear orderings between these four cardinalities. We show that at least five of the six possible linear orderings are consistent with ZF.
Lorenz Halbeisen, Riccardo Plati, Salome Schumacher, Saharon Shelah
Ann. Pure Appl. Log.2