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identity_type [2014/11/17 19:48] nikolaj ^^ |
identity_type [2016/04/12 15:42] nikolaj |
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| ==== Intension, extension ==== | ==== Intension, extension ==== | ||
| + | See [[http://mathoverflow.net/questions/156238/function-extensionality-does-it-make-a-difference-why-would-one-keep-it-out-of | ||
| + | | Andrej Bauer on intentional equality]] | ||
| + | |||
| === The concept === | === The concept === | ||
| There is a correspondence between a predicate $P$ over a class of objects and it's //extension// $\{x\ |\ P(x)\}$. The latter is the collection of objects it describes. | There is a correspondence between a predicate $P$ over a class of objects and it's //extension// $\{x\ |\ P(x)\}$. The latter is the collection of objects it describes. | ||
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| We see that intensionally different definition can have the same extension. | We see that intensionally different definition can have the same extension. | ||
| + | |||
| + | Another remark: | ||
| + | We have $2(12+15)=2*3*4+2*3*5=3(8+10)$, and while $2(12+15)\mapsto 24+30$ and $3(8+10)\mapsto 24+30$ feel like natural reductions, $2(12+15)\mapsto 3(8+10)$ feels random. That is to say, there is a sort of computational direction that comes with a formulized evaluation. | ||
| === In theories === | === In theories === | ||
| Line 98: | Line 104: | ||
| === Reference === | === Reference === | ||
| - | nLab: [[http://ncatlab.org/nlab/show/identity+type|identity type]] | + | nLab: |
| + | [[http://ncatlab.org/nlab/show/identity+type|identity type]] | ||
| + | |||
| + | StackExchange: | ||
| + | [[http://mathoverflow.net/questions/156238/function-extensionality-does-it-make-a-difference-why-would-one-keep-it-out-of | ||
| + | | Andrej Bauer on intentional equality]] | ||
| ==== Parents ==== | ==== Parents ==== | ||
| === Related === | === Related === | ||
| [[Dependent type theory]] | [[Dependent type theory]] | ||
