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25
A proof of the Kepler conjecture
 Math. Intelligencer
, 1994
"... This section describes the structure of the proof of ..."
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This section describes the structure of the proof of
MetiTarski: An Automatic Theorem Prover for RealValued Special Functions
"... Abstract Many theorems involving special functions such as ln, exp and sin can be proved automatically by MetiTarski: a resolution theorem prover modified to call a decision procedure for the theory of real closed fields. Special functions are approximated by upper and lower bounds, which are typica ..."
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Abstract Many theorems involving special functions such as ln, exp and sin can be proved automatically by MetiTarski: a resolution theorem prover modified to call a decision procedure for the theory of real closed fields. Special functions are approximated by upper and lower bounds, which are typically rational functions derived from Taylor or continued fraction expansions. The decision procedure simplifies clauses by deleting literals that are inconsistent with other algebraic facts. MetiTarski simplifies arithmetic expressions by conversion to a recursive representation, followed by flattening of nested quotients. Applications include verifying hybrid and control systems.
Verifying nonlinear real formulas via sums of squares
 Theorem Proving in Higher Order Logics, TPHOLs 2007, volume 4732 of Lect. Notes in Comp. Sci
, 2007
"... Abstract. Techniques based on sums of squares appear promising as a general approach to the universal theory of reals with addition and multiplication, i.e. verifying Boolean combinations of equations and inequalities. A particularly attractive feature is that suitable ‘sum of squares ’ certificates ..."
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Abstract. Techniques based on sums of squares appear promising as a general approach to the universal theory of reals with addition and multiplication, i.e. verifying Boolean combinations of equations and inequalities. A particularly attractive feature is that suitable ‘sum of squares ’ certificates can be found by sophisticated numerical methods such as semidefinite programming, yet the actual verification of the resulting proof is straightforward even in a highly foundational theorem prover. We will describe our experience with an implementation in HOL Light, noting some successes as well as difficulties. We also describe a new approach to the univariate case that can handle some otherwise difficult examples. 1 Verifying nonlinear formulas over the reals Over the real numbers, there are algorithms that can in principle perform quantifier elimination from arbitrary firstorder formulas built up using addition, multiplication and the usual equality and inequality predicates. A classic example of such a quantifier elimination equivalence is the criterion for a quadratic equation to have a real root: ∀a b c. (∃x. ax 2 + bx + c = 0) ⇔ a = 0 ∧ (b = 0 ⇒ c = 0) ∨ a � = 0 ∧ b 2 ≥ 4ac
The Flyspeck Project
"... Abstract. This article gives an introduction to a longterm project called Flyspeck, whose purpose is to give a formal verification of the ..."
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Abstract. This article gives an introduction to a longterm project called Flyspeck, whose purpose is to give a formal verification of the
A HOL theory of Euclidean space
 In Hurd and Melham [7
, 2005
"... Abstract. We describe a formalization of the elementary algebra, topology and analysis of finitedimensional Euclidean space in the HOL Light theorem prover. (Euclidean space is R N with the usual notion of distance.) A notable feature is that the HOL type system is used to encode the dimension N in ..."
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Abstract. We describe a formalization of the elementary algebra, topology and analysis of finitedimensional Euclidean space in the HOL Light theorem prover. (Euclidean space is R N with the usual notion of distance.) A notable feature is that the HOL type system is used to encode the dimension N in a simple and useful way, even though HOL does not permit dependent types. In the resulting theory the HOL type system, far from getting in the way, naturally imposes the correct dimensional constraints, e.g. checking compatibility in matrix multiplication. Among the interesting later developments of the theory are a partial decision procedure for the theory of vector spaces (based on a more general algorithm due to Solovay) and a formal proof of various classic theorems of topology and analysis for arbitrary Ndimensional Euclidean space, e.g. Brouwer’s fixpoint theorem and the differentiability of inverse functions. 1 1 The problem with R N
Real World Verification
"... Abstract. Scalable handling of real arithmetic is a crucial part of the verification of hybrid systems, mathematical algorithms, and mixed analog/digital circuits. Despite substantial advances in verification technology, complexity issues with classical decision procedures are still a major obstacle ..."
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Abstract. Scalable handling of real arithmetic is a crucial part of the verification of hybrid systems, mathematical algorithms, and mixed analog/digital circuits. Despite substantial advances in verification technology, complexity issues with classical decision procedures are still a major obstacle for formal verification of realworld applications, e.g., in automotive and avionic industries. To identify strengths and weaknesses, we examine state of the art symbolic techniques and implementations for the universal fragment of realclosed fields: approaches based on quantifier elimination, Gröbner Bases, and semidefinite programming for the Positivstellensatz. Within a uniform context of the verification tool KeYmaera, we compare these approaches qualitatively and quantitatively on verification benchmarks from hybrid systems, textbook algorithms, and on geometric problems. Finally, we introduce a new decision procedure combining Gröbner Bases and semidefinite programming for the real Nullstellensatz that outperforms the individual approaches on an interesting set of problems.
Towards Automatic Proofs of Inequalities Involving Elementary Functions
 In Pragmatics of Decision Procedures in Automated Reasoning (PDPAR
, 2006
"... Inequalities involving functions such as sines, exponentials and logarithms lie outside the scope of decision procedures, and can only be solved using heuristic methods. Preliminary investigations suggest that many such problems can be solved by reduction to algebraic inequalities, which can then be ..."
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Inequalities involving functions such as sines, exponentials and logarithms lie outside the scope of decision procedures, and can only be solved using heuristic methods. Preliminary investigations suggest that many such problems can be solved by reduction to algebraic inequalities, which can then be decided by a decision procedure for the theory of real closed fields (RCF). The reduction involves replacing each occurrence of a function by a lower or upper bound (as appropriate) typically derived from a power series expansion. Typically this requires splitting the domain of the function being replaced, since most bounds are only valid for specific intervals. 1
Combined Decision Techniques for the Existential Theory of the Reals
 CALCULEMUS
, 2009
"... Methods for deciding quantifierfree nonlinear arithmetical conjectures over *** are crucial in the formal verification of many realworld systems and in formalised mathematics. While nonlinear (rational function) arithmetic over *** is decidable, it is fundamentally infeasible: any general decisi ..."
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Methods for deciding quantifierfree nonlinear arithmetical conjectures over *** are crucial in the formal verification of many realworld systems and in formalised mathematics. While nonlinear (rational function) arithmetic over *** is decidable, it is fundamentally infeasible: any general decision method for this problem is worstcase exponential in the dimension (number of variables) of the formula being analysed. This is unfortunate, as many practical applications of real algebraic decision methods require reasoning about highdimensional conjectures. Despite their inherent infeasibility, a number of different decision methods have been developed, most of which have "sweet spots"  e.g., types of problems for which they perform much better than they do in general. Such "sweet spots" can in many cases be heuristically combined to solve problems that are out of reach of the individual decision methods when used in isolation. RAHD ("Real Algebra in High Dimensions") is a theorem prover that works to combine a collection of real algebraic decision methods in ways that exploit their respective "sweetspots." We discuss highlevel mathematical and design aspects of RAHD and illustrate its use on a number of examples.
Combining decision procedures for the reals
 In preparation
"... Vol. 2 (4:4) 2006, pp. 1–42 www.lmcsonline.org ..."
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