Difference between revisions of "Recursive function theory"
EndreyMark (talk | contribs) (Categorizing under Category:Theoretical foundations. And some minor rephrasings.) |
EndreyMark (talk | contribs) m (Headline hierarchy is simpified -- a ,,singleton'' level eliminated) |
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Well-known concepts are taken from [Mon:MatLog], but several new notations (only notations, not concepts) are introduced to reflect all concepts described in [Mon:MatLog], and some simplification are made (by allowing zero-arity generalizations). These are plans to achive formalizations that can allow us in the future to incarnate the main concepts of recursive function theory in a programming language. |
Well-known concepts are taken from [Mon:MatLog], but several new notations (only notations, not concepts) are introduced to reflect all concepts described in [Mon:MatLog], and some simplification are made (by allowing zero-arity generalizations). These are plans to achive formalizations that can allow us in the future to incarnate the main concepts of recursive function theory in a programming language. |
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− | + | == Primitive recursive functions == |
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− | + | === Type system === |
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:<math>\left\lfloor0\right\rfloor = \mathbb N</math> |
:<math>\left\lfloor0\right\rfloor = \mathbb N</math> |
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:<math>\begin{matrix}\left\lfloor n + 1\right\rfloor = \underbrace{\mathbb N\times\dots\times\mathbb N}\to\mathbb N\\\;\;\;\;\;\;\;\;n+1\end{matrix}</math> |
:<math>\begin{matrix}\left\lfloor n + 1\right\rfloor = \underbrace{\mathbb N\times\dots\times\mathbb N}\to\mathbb N\\\;\;\;\;\;\;\;\;n+1\end{matrix}</math> |
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− | + | === Base functions === |
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− | + | ==== Constant ==== |
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:<math>\mathbf 0 : \left\lfloor0\right\rfloor</math> |
:<math>\mathbf 0 : \left\lfloor0\right\rfloor</math> |
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Does it take a generalization to allow, or can it be inferred? |
Does it take a generalization to allow, or can it be inferred? |
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− | + | ==== Succesor function ==== |
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:<math>\mathbf s : \left\lfloor1\right\rfloor</math> |
:<math>\mathbf s : \left\lfloor1\right\rfloor</math> |
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:<math>\mathbf s = \lambda x . x + 1</math> |
:<math>\mathbf s = \lambda x . x + 1</math> |
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− | + | ==== Projection functions ==== |
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For all <math>0\leq i<m</math>: |
For all <math>0\leq i<m</math>: |
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:<math>\mathbf U^m_i x_0\dots x_i \dots x_{m-1} = x_i</math> |
:<math>\mathbf U^m_i x_0\dots x_i \dots x_{m-1} = x_i</math> |
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− | + | === Operations === |
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− | + | ==== Composition ==== |
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:<math>\underline\mathbf\dot K^m_n : \left\lfloor m\right\rfloor \times \left\lfloor n\right\rfloor^m \to \left\lfloor n\right\rfloor</math> |
:<math>\underline\mathbf\dot K^m_n : \left\lfloor m\right\rfloor \times \left\lfloor n\right\rfloor^m \to \left\lfloor n\right\rfloor</math> |
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:<math>\underline\mathbf K^m_n f g_0\dots g_{m-1} x_0 \dots x_{n-1} = \mathbf \Phi^n_m f g_0 \dots g_{m-1} x_0 \dots x_{n-1}</math> |
:<math>\underline\mathbf K^m_n f g_0\dots g_{m-1} x_0 \dots x_{n-1} = \mathbf \Phi^n_m f g_0 \dots g_{m-1} x_0 \dots x_{n-1}</math> |
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− | + | ==== Primitive recursion ==== |
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:<math>\underline\mathbf R^m : \left\lfloor m\right\rfloor \times \left\lfloor m+2\right\rfloor \to \left\lfloor m+1\right\rfloor</math> |
:<math>\underline\mathbf R^m : \left\lfloor m\right\rfloor \times \left\lfloor m+2\right\rfloor \to \left\lfloor m+1\right\rfloor</math> |
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:<math>g x_0 \dots x_{m-1} \left(\mathbf s y\right) = \mathbf S_{m+1} h g x_0 \dots x_{m-1} y</math> |
:<math>g x_0 \dots x_{m-1} \left(\mathbf s y\right) = \mathbf S_{m+1} h g x_0 \dots x_{m-1} y</math> |
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− | + | == General recursive functions == |
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Everything seen above, and the new concepts: |
Everything seen above, and the new concepts: |
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− | + | === Type system === |
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:<math> \widehat{\,m\,} = \left\{ f : \left\lfloor m+1\right\rfloor\;\vert\;f \mathrm{\ is\ special}\right\}</math> |
:<math> \widehat{\,m\,} = \left\{ f : \left\lfloor m+1\right\rfloor\;\vert\;f \mathrm{\ is\ special}\right\}</math> |
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− | + | === Operations === |
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− | + | ==== Minimalization ==== |
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:<math>\underline\mu^m : \widehat m \to \left\lfloor m\right\rfloor</math> |
:<math>\underline\mu^m : \widehat m \to \left\lfloor m\right\rfloor</math> |
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:<math>\underline\mu^m f = \min \left\{y\in\mathbb N\;\vert\;f x_0 \dots x_{m-1} y = 0\right\}</math> |
:<math>\underline\mu^m f = \min \left\{y\in\mathbb N\;\vert\;f x_0 \dots x_{m-1} y = 0\right\}</math> |
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Minimalization does not lead us out of the word of total functions, if we use it only for special functions -- the property of being special is defined exactly for this purpose [Mon:MatLog, 45]. |
Minimalization does not lead us out of the word of total functions, if we use it only for special functions -- the property of being special is defined exactly for this purpose [Mon:MatLog, 45]. |
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+ | |||
− | + | == Partial recursive functions == |
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Everything seen above, but new constructs are provided, too. |
Everything seen above, but new constructs are provided, too. |
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− | + | === Type system === |
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:<math>\begin{matrix}\left\lceil n + 1\right\rceil = \underbrace{\mathbb N\times\dots\times\mathbb N}\supset\!\to\mathbb N\\\;\;\;\;\;\;n+1\end{matrix}</math> |
:<math>\begin{matrix}\left\lceil n + 1\right\rceil = \underbrace{\mathbb N\times\dots\times\mathbb N}\supset\!\to\mathbb N\\\;\;\;\;\;\;n+1\end{matrix}</math> |
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<math>\left\lceil0\right\rceil</math> in another way than simply <math>\left\lceil0\right\rceil = \left\lfloor0\right\rfloor = \mathbb N</math>? Partial constants? |
<math>\left\lceil0\right\rceil</math> in another way than simply <math>\left\lceil0\right\rceil = \left\lfloor0\right\rfloor = \mathbb N</math>? Partial constants? |
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− | + | === Operations === |
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+ | |||
:<math>\overline\mathbf\dot K^m_n : \left\lceil m\right\rceil \times \left\lceil n\right\rceil^m \to \left\lceil n\right\rceil</math> |
:<math>\overline\mathbf\dot K^m_n : \left\lceil m\right\rceil \times \left\lceil n\right\rceil^m \to \left\lceil n\right\rceil</math> |
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:<math>\overline\mathbf R^m : \left\lceil m\right\rceil \times \left\lceil m+2\right\rceil \to \left\lceil m+1\right\rceil</math> |
:<math>\overline\mathbf R^m : \left\lceil m\right\rceil \times \left\lceil m+2\right\rceil \to \left\lceil m+1\right\rceil</math> |
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== Bibliography == |
== Bibliography == |
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;<nowiki>[HasFeyCr:CombLog1]</nowiki> |
;<nowiki>[HasFeyCr:CombLog1]</nowiki> |
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:Curry, Haskell B; Feys, Robert; Craig, William: Combinatory Logic. Volume I. North-Holland Publishing Company, Amsterdam, 1958. |
:Curry, Haskell B; Feys, Robert; Craig, William: Combinatory Logic. Volume I. North-Holland Publishing Company, Amsterdam, 1958. |
Revision as of 17:17, 23 April 2006
Introduction
Plans towards a programming language
Well-known concepts are taken from [Mon:MatLog], but several new notations (only notations, not concepts) are introduced to reflect all concepts described in [Mon:MatLog], and some simplification are made (by allowing zero-arity generalizations). These are plans to achive formalizations that can allow us in the future to incarnate the main concepts of recursive function theory in a programming language.
Primitive recursive functions
Type system
Base functions
Constant
Question: is the well-known approach superfluous? Can we avoid it and use the more simple and indirect approach, if we generalize operations (especially composition) to deal with zero-arity cases in an approprate way? E.g., and , too? Does it take a generalization to allow, or can it be inferred?
Succesor function
Projection functions
For all :
Operations
Composition
This resembles to the combinator of Combinatory logic (as described in [HasFeyCr:CombLog1, 171]). If we prefer avoiding the notion of the nested tuple, and use a more homogenous style (somewhat resembling to currying):
Let underbrace not mislead us -- it does not mean any bracing.
remembering us to
Primitive recursion
The last equation resembles to the combinator of Combinatory logic (as described in [HasFeyCr:CombLog1, 169]):
General recursive functions
Everything seen above, and the new concepts:
Type system
See the definition of being special [Mon:MathLog, 45]. This property ensures, that minimalization does not lead us out of the world of total functions. Its definition is the rather straightforward formalization of this expectation.
Operations
Minimalization
Minimalization does not lead us out of the word of total functions, if we use it only for special functions -- the property of being special is defined exactly for this purpose [Mon:MatLog, 45].
Partial recursive functions
Everything seen above, but new constructs are provided, too.
Type system
Question: is there any sense to define in another way than simply ? Partial constants?
Operations
Their definitions are straightforward.
Bibliography
- [HasFeyCr:CombLog1]
- Curry, Haskell B; Feys, Robert; Craig, William: Combinatory Logic. Volume I. North-Holland Publishing Company, Amsterdam, 1958.
- [Mon:MathLog]
- Monk, J. Donald: Mathematical Logic. Springer-Verlag, New York * Heidelberg * Berlin, 1976.