Decidability of the Equational Theory of the Continuous Geometry $CG(\Bbb {F})$
نویسنده
چکیده
Let F be the field of real or complex numbers. For n ≥ 1, the subspaces of the n-dimensional inner product space F form a modular ortholattice PGn−1(F), or simply PGn−1. This lattice has a normalized dimension function dn : PGn−1 → [0, 1] that associates to a subspace A, its dimension divided by n. von Neumann [7] showed there is an embedding PGn−1 ↪→ PG2n−1 that preserves normalized dimensions. So the inductive limit of the chain PG1 ↪→ PG3 ↪→ PG7 ↪→ · · · yields a modular ortholattice PG∞(F), or simply PG∞. This ortholattice PG∞ also has a dimension function, so is a metric lattice [1], and its metric space completion is a complete modular ortholattice CG(F), or simply CG. This CG was von Neumann’s first example of a continuous geometry. Our purpose is to show the equational theory of CG is decidable. The key tools are results of Herrmann and Roddy [3] on equations in modular ortholattices, and of Dunn, Hagge, Moss, and Wang [6] showing the first order theory of each PGn is decidable.
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ورودعنوان ژورنال:
- J. Philosophical Logic
دوره 42 شماره
صفحات -
تاریخ انتشار 2013