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A thread of HOL development
 Computer Journal
"... The HOL system is a mechanized proof assistant for higher order logic that has been under continuous development since the mid1980s, by an everchanging group of developers and external contributors. We give a brief overview of various implementations of the HOL logic before focusing on the evoluti ..."
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The HOL system is a mechanized proof assistant for higher order logic that has been under continuous development since the mid1980s, by an everchanging group of developers and external contributors. We give a brief overview of various implementations of the HOL logic before focusing on the evolution of certain important features available in a recent implementation. We also illustrate how the module system of Standard ML provided security and modularity in the construction of the HOL kernel, as well as serving in a separate capacity as a useful representation medium for persistent, hierarchical logical theories.
An Irrational Construction of R from Z
"... This paper reports on a construction of the real numbers in the ProofPower implementation of the HOL logic. Since the original construction was implemented, some major improvements to the ideas have been discovered. The improvements involve some entertaining mathematics: it turns out that the De ..."
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This paper reports on a construction of the real numbers in the ProofPower implementation of the HOL logic. Since the original construction was implemented, some major improvements to the ideas have been discovered. The improvements involve some entertaining mathematics: it turns out that the Dedekind cuts provide many routes one can travel to get from the ring of integers, Z, to the eld of real numbers, R.
1.1 Automated Theorem Proving Background
"... Abstract. This paper reports on a construction of the real numbers in the ProofPower implementation of the HOL logic. Since the original construction was implemented, some major improvements to the ideas have been discovered. The improvements involve some entertaining mathematics: it turns out that ..."
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Abstract. This paper reports on a construction of the real numbers in the ProofPower implementation of the HOL logic. Since the original construction was implemented, some major improvements to the ideas have been discovered. The improvements involve some entertaining mathematics: it turns out that the Dedekind cuts provide many routes one can travel to get from the ring of integers, Z, to the field of real numbers, R. The traditional stopover on the way is the field of rational numbers, Q. This paper shows that going via certain rings of algebraic numbers can provide a pleasant alternative to the more welltrodden track.
Doktors der Naturwissenschaften (Dr. rer. nat.) genehmigten Dissertation.
"... Abstract This thesis addresses two basic problems with the current crop of mechanized proof systems. The first problem is largely technical: the act of soundly introducing a recursive definition is not as simple and direct as it should be. The second problem is largely social: there is very little c ..."
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Abstract This thesis addresses two basic problems with the current crop of mechanized proof systems. The first problem is largely technical: the act of soundly introducing a recursive definition is not as simple and direct as it should be. The second problem is largely social: there is very little codesharing between theorem prover implementations; as a result, common facilities are typically built anew in each proof system, and the overall progress of the field is thereby hampered. We use the application domain of functional programming to explore the first problem. We build a patternmatching style recursive function definition facility, based on mechanically proven wellfounded recursion and induction theorems. Reasoning support is embodied by automatically derived induction theorems, which are customised to the recursion structure of definitions. This provides a powerful, guaranteed sound, definitionandreasoning facility for functions that strongly resemble programs in languages such as ML or Haskell. We demonstrate this package (called TFL) on several wellknown challenge problems. In spite of its power, the approach suffers from a low level of automation, because a termination relation must be supplied at function definition time. If humans are to be largely relieved of the task of proving termination, it must be possible for the act of defining a recursive function to be completely separate from the act of finding a termination relation for it and proving the ensuing termination conditions. We show how this separation can be achieved, while still preserving soundness. Building on this, we present a new way to define program schemes and prove highlevel program transformations.