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A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
.
.
Zariski Geometries, Lecture 1
Masanori Itai
Dept of Math Sci, Tokai University, Japan
August 30, 2011 at Kobe university
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
References
HZ96 Ehud Hrushovski, Boris Zilber, Zariski geometries, J of theAMS, 1996
Z10 B. Zilber, Zariski Geometries , London Math. Soc. Lect NoteSer. 360, Cambridge, 2010
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Table of Contents
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1 A little bit of History
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. .
2 Topological Structures with good dimension
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. .
3 Quantifier Elimination
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4 Elementary extensions
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Zilber Conjecture
Strongly minimal
trivial (no structure)linear (locally modular) : vector spacesnon-linear (non-locally modular) : alg. closed fields
Zilber conjectured that any non-locally modular stronglyminimal set interprets an acf!
Counter example was constructed by Hrushovski usinggeneric model construction.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Zilber Conjecture
Strongly minimal
trivial (no structure)linear (locally modular) : vector spacesnon-linear (non-locally modular) : alg. closed fields
Zilber conjectured that any non-locally modular stronglyminimal set interprets an acf!
Counter example was constructed by Hrushovski usinggeneric model construction.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Zilber Conjecture
Strongly minimal
trivial (no structure)linear (locally modular) : vector spacesnon-linear (non-locally modular) : alg. closed fields
Zilber conjectured that any non-locally modular stronglyminimal set interprets an acf!
Counter example was constructed by Hrushovski usinggeneric model construction.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
ZC is true for Zariski geometries
In algebraic geometry; algebraically closed field⇒ Zariskitopology, dimension notion
Model theory of Zariski structures; Noetherian topology,dmension notion⇒ algebraically closed field
Ample (non-linear, non-locally modular) Zariski geometryinterprets an algebraically closed field.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
ZC is true for Zariski geometries
In algebraic geometry; algebraically closed field⇒ Zariskitopology, dimension notion
Model theory of Zariski structures; Noetherian topology,dmension notion⇒ algebraically closed field
Ample (non-linear, non-locally modular) Zariski geometryinterprets an algebraically closed field.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
ZC is true for Zariski geometries
In algebraic geometry; algebraically closed field⇒ Zariskitopology, dimension notion
Model theory of Zariski structures; Noetherian topology,dmension notion⇒ algebraically closed field
Ample (non-linear, non-locally modular) Zariski geometryinterprets an algebraically closed field.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Topological structures, p. 12
Consider a collection of topological spaces {M n : n ∈ N}.each Mn is Noetherian
proj is continuous
graph of equality is closed
fibers of closed sets are closed
Cartesian products of closed sets is closed
etc
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Good dimension
In subsection 3.1.1, we have a list of postulates for the dimesionnotion;
(DP) dimesion of a point
(DU) dimension of unions
(SI) strong irreducibility
(AF) addition formula
(FC) fiber condition
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Zariski structures
.
Definition (Def 3.1.3)
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{M n : n ∈ N} is Zariski structures if
Noetherian topology
dimension notion
semi-proper :Let S ⊆cl M n be irreducible, then there exists a proper closed
subsetF ⊂ prSsuch that
prS− F ⊆ prS
.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Zariski geometry
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Definition (Def 3.5.2)
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Zariski geometry= Zariski structure+ (sPS)+ (EU)
(sPS) : strongly Pre-Smooth
(EU) : Essentially Uncountable
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
.
Theorem (Thm 3.6.21)
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A one-dimensional, uncountable, pre-smooth, irreducible ZariskistructureM is a Zariski geometry.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Basic Examples (1)
Algebraic varaity M over an acf. (Thm 3.4.1)Zariski structure is complete (ie. projection of closed is closed)if M is.(PS), pre-smooth if M is.(EU), essentially uncountable, if M .
Compact complex manifold M with the notion of analyticdimension. It satisfies (PS) and (EU). (Thm 3.4.3)
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Basic Examples (1)
Algebraic varaity M over an acf. (Thm 3.4.1)Zariski structure is complete (ie. projection of closed is closed)if M is.(PS), pre-smooth if M is.(EU), essentially uncountable, if M .
Compact complex manifold M with the notion of analyticdimension. It satisfies (PS) and (EU). (Thm 3.4.3)
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Basic Examples (2)
Proper varieties of rigid anlaytic geometry (Thm 3.4.7)
Definable sets of finite Morley rank and Morley degree 1 indifferentially closed fields. (Thm 3.4.9, Pillay)
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Basic Examples (2)
Proper varieties of rigid anlaytic geometry (Thm 3.4.7)
Definable sets of finite Morley rank and Morley degree 1 indifferentially closed fields. (Thm 3.4.9, Pillay)
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Semi-properness
M is a Zariski structure.
We want the theory of the structure M to have the elimination ofquantifiers.For this, semi-properness axiom is needed:
.
Definition (SP)
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.
.
Let S ⊆cl M n be irreducible, then there exists a proper closed
subset F ⊂ prS such that
prS− F ⊆ prS
.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
QE for Zariski structures
.
Theorem (Thm 3.2.1)
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.
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A Zariski structureM admits elimination of quantifiers; that is anydefinable ssubsetQ ⊆ M n is constructible, i.e., boolean conbinationof closed sets.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Proof of QE (1)
We must show that the projection of a constructible subset isconstructible.
For this let Q = S− P where both S, P closed.
We show the theorem by induction on dim S.
LetdS = min{dim S(a, M) : a ∈ prS},F = {b ∈ prS : dim P(b, M) ≥ dS}.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Proof of QE (2)
Let F be the closure of F.
F is a proper closed subset of prS, by (FC).
Since prS is irreducible, we have
dim F < dim prS.
Let S′ = S∩ pr−1(F).
Since F ∩ pr(S) , pr(S), we have S′ ( S.
Thus, dim S′ < dim S.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Proof of QE (2)
Let F be the closure of F.
F is a proper closed subset of prS, by (FC).
Since prS is irreducible, we have
dim F < dim prS.
Let S′ = S∩ pr−1(F).
Since F ∩ pr(S) , pr(S), we have S′ ( S.
Thus, dim S′ < dim S.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Proof of QE (2)
Let F be the closure of F.
F is a proper closed subset of prS, by (FC).
Since prS is irreducible, we have
dim F < dim prS.
Let S′ = S∩ pr−1(F).
Since F ∩ pr(S) , pr(S), we have S′ ( S.
Thus, dim S′ < dim S.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Proof of QE (2)
Let F be the closure of F.
F is a proper closed subset of prS, by (FC).
Since prS is irreducible, we have
dim F < dim prS.
Let S′ = S∩ pr−1(F).
Since F ∩ pr(S) , pr(S), we have S′ ( S.
Thus, dim S′ < dim S.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Proof of QE (2)
Let F be the closure of F.
F is a proper closed subset of prS, by (FC).
Since prS is irreducible, we have
dim F < dim prS.
Let S′ = S∩ pr−1(F).
Since F ∩ pr(S) , pr(S), we have S′ ( S.
Thus, dim S′ < dim S.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Proof of QE (2)
Let F be the closure of F.
F is a proper closed subset of prS, by (FC).
Since prS is irreducible, we have
dim F < dim prS.
Let S′ = S∩ pr−1(F).
Since F ∩ pr(S) , pr(S), we have S′ ( S.
Thus, dim S′ < dim S.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Proof of QE (3)
Notice that pr(Q) = pr(S− P) ⊆ pr(S′ − P) ∪ pr(S− F).
If b ∈ pr(S− P), then P(b, M) ( S(b, M). Thus
(prS− F) ⊆ prQ.
Therefore, pr(Q) = pr(S− P) = pr(S− P) ∪ (pr(S) − F).
Notice that pr(S) − F is already in the desired form byinduction hypothesis.
Apply induction to S− P to finish the proof.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Proof of QE (3)
Notice that pr(Q) = pr(S− P) ⊆ pr(S′ − P) ∪ pr(S− F).
If b ∈ pr(S− P), then P(b, M) ( S(b, M). Thus
(prS− F) ⊆ prQ.
Therefore, pr(Q) = pr(S− P) = pr(S− P) ∪ (pr(S) − F).
Notice that pr(S) − F is already in the desired form byinduction hypothesis.
Apply induction to S− P to finish the proof.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Proof of QE (3)
Notice that pr(Q) = pr(S− P) ⊆ pr(S′ − P) ∪ pr(S− F).
If b ∈ pr(S− P), then P(b, M) ( S(b, M). Thus
(prS− F) ⊆ prQ.
Therefore, pr(Q) = pr(S− P) = pr(S− P) ∪ (pr(S) − F).
Notice that pr(S) − F is already in the desired form byinduction hypothesis.
Apply induction to S− P to finish the proof.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Proof of QE (3)
Notice that pr(Q) = pr(S− P) ⊆ pr(S′ − P) ∪ pr(S− F).
If b ∈ pr(S− P), then P(b, M) ( S(b, M). Thus
(prS− F) ⊆ prQ.
Therefore, pr(Q) = pr(S− P) = pr(S− P) ∪ (pr(S) − F).
Notice that pr(S) − F is already in the desired form byinduction hypothesis.
Apply induction to S− P to finish the proof.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Proof of QE (3)
Notice that pr(Q) = pr(S− P) ⊆ pr(S′ − P) ∪ pr(S− F).
If b ∈ pr(S− P), then P(b, M) ( S(b, M). Thus
(prS− F) ⊆ prQ.
Therefore, pr(Q) = pr(S− P) = pr(S− P) ∪ (pr(S) − F).
Notice that pr(S) − F is already in the desired form byinduction hypothesis.
Apply induction to S− P to finish the proof.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
QE for Zariski geometry
.
Proposition (Prop 3.3.7)
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M : one-dimensional Zariski Geometry. Then the theory ofM admitsquantifier elimination.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Axioms for one-dimensional Zariski geometry, p. 31
(Z1) (QE) prS ⊇ prS− F, for some proper closed F ⊂cl prS
(Z2) (SM) For S ⊆cl M n+1, there is m such that for all a ∈ M n
S(a) = M or |S(a)| ≤ m
(Z3) dim M n ≤ n.Given a closed irreducible S ⊆ M n. Every component of thediagonal F ∩ {xi = x j} is of dimension ≥ dim S− 1.
.
Remark
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.
.
These are the axioms given in the paper [HZ].
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
strong minimality
.
Corollary (Cor 3.3.8)
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.
.
M is strongly minimal.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Proof of S.M. with (Z2)
Let E ⊆ M n × M be definable.
Show E(a) is finite or co-finite, with a uniform bound for alla ∈ M n.
WLOG, E = S− F, with S, F closed.
If S(a) is finite, then E(a) is finite with the same bound.
Apply (Z2) to both S, F to finish the proof.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Proof of S.M. with (Z2)
Let E ⊆ M n × M be definable.
Show E(a) is finite or co-finite, with a uniform bound for alla ∈ M n.
WLOG, E = S− F, with S, F closed.
If S(a) is finite, then E(a) is finite with the same bound.
Apply (Z2) to both S, F to finish the proof.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Proof of S.M. with (Z2)
Let E ⊆ M n × M be definable.
Show E(a) is finite or co-finite, with a uniform bound for alla ∈ M n.
WLOG, E = S− F, with S, F closed.
If S(a) is finite, then E(a) is finite with the same bound.
Apply (Z2) to both S, F to finish the proof.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Proof of S.M. with (Z2)
Let E ⊆ M n × M be definable.
Show E(a) is finite or co-finite, with a uniform bound for alla ∈ M n.
WLOG, E = S− F, with S, F closed.
If S(a) is finite, then E(a) is finite with the same bound.
Apply (Z2) to both S, F to finish the proof.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Proof of S.M. with (Z2)
Let E ⊆ M n × M be definable.
Show E(a) is finite or co-finite, with a uniform bound for alla ∈ M n.
WLOG, E = S− F, with S, F closed.
If S(a) is finite, then E(a) is finite with the same bound.
Apply (Z2) to both S, F to finish the proof.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Language
M : Zariski structure
C ⊆ M n is closed, introduce a predicate symbol for eachclosed C ⊆ M n
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
elementary extensions (1)
.
Definition (Def 3.5.16)
.
.
.
a-closed : LetS(x, y) be l + m-ary closed set.S ⊆ M ′l .Postulate that eachS(a, M ′m) is closed inM ′m.This gives the topology on eachM ′.Dimension
dim S(a, M ′) = max{k ∈ N : a ∈ P(S, k)} + 1
whereP(S, k) = {a ∈ prS : dim S∩ pr−1(a) > k}.
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
elementary extensions (2)
.
Theorem (Thm 3.5.25)
.
.
.
M : Zariski structure satisfying (EU)
M � M ′
M ′ : Zariski structure
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Summary
Start with M : Noerthrian topology + dimension notion
Introduce language for M , hence model theory of M ispossible
Theory of M admits quantifier elimination
M is strongly minimal
Elementary extension of M is Zariski structure (geometry)
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Summary
Start with M : Noerthrian topology + dimension notion
Introduce language for M , hence model theory of M ispossible
Theory of M admits quantifier elimination
M is strongly minimal
Elementary extension of M is Zariski structure (geometry)
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Summary
Start with M : Noerthrian topology + dimension notion
Introduce language for M , hence model theory of M ispossible
Theory of M admits quantifier elimination
M is strongly minimal
Elementary extension of M is Zariski structure (geometry)
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Summary
Start with M : Noerthrian topology + dimension notion
Introduce language for M , hence model theory of M ispossible
Theory of M admits quantifier elimination
M is strongly minimal
Elementary extension of M is Zariski structure (geometry)
Masanori Itai Zariski Geometries, Lecture 1
A little bit of HistoryTopological Structures with good dimension
Quantifier EliminationElementary extensions
Summary
Start with M : Noerthrian topology + dimension notion
Introduce language for M , hence model theory of M ispossible
Theory of M admits quantifier elimination
M is strongly minimal
Elementary extension of M is Zariski structure (geometry)
Masanori Itai Zariski Geometries, Lecture 1