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Embedding theorems for spaces of ℝ-places of rational function fields and their products

Katarzyna Kuhlmann, Franz-Viktor Kuhlmann (2012)

Fundamenta Mathematicae

We study spaces M(R(y)) of ℝ-places of rational function fields R(y) in one variable. For extensions F|R of formally real fields, with R real closed and satisfying a natural condition, we find embeddings of M(R(y)) in M(F(y)) and prove uniqueness results. Further, we study embeddings of products of spaces of the form M(F(y)) in spaces of ℝ-places of rational function fields in several variables. Our results uncover rather unexpected obstacles to a positive solution of the open question whether the...

Every reasonably sized matrix group is a subgroup of S ∞

Robert Kallman (2000)

Fundamenta Mathematicae

Every reasonably sized matrix group has an injective homomorphism into the group S of all bijections of the natural numbers. However, not every reasonably sized simple group has an injective homomorphism into S .

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