Affiliation:
1. Sobolev Institute of Mathematics ; Novosibirsk State University
Abstract
We prove the existence of 2ω pairwise non-Σ-embeddable into each other (and henceforth non-Σ-isomorphic) Σ-presentations of the additive group of the real numbers in the hereditarily finite superstructure over the ordered field of the real numbers.
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