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by defrost2 hours ago |
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upvoteby Jtsummers1 hours ago|
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You need a way to differentiate the two 5s, that isn't present. If you had a list like:

  L = [(5,foo), (2,bar), (2,baz),...]
And did a:

  SORT(L, key=first) # or however it'd be specified
Then the duplicate 2s would be fine, because they're no longer duplicates, only duplicate keys. But it would still fail if (2,baz) showed up twice in the source and destination even though we've asked for SORT, not UNIQSORT.
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upvoteby defrost1 hours ago|
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More seriously,

> You need a way to differentiate the two 5s

As there's no unique filtering or other reduction going on here, there's a permutation chain from input to output.

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upvoteby Jtsummers37 minutes ago|
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But that's not in the specification given above. That specification is entirely wrong to specify SORT. It requires no duplicates survive the sorting process.
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upvoteby defrost1 hours ago|
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In the cases of

  SORT ( 3, 2, 5, 5 ) ->> ( 2, 3, 5, 5 ) and
  SORT ( 3, 2, 5, 5 ) ->> ( 2, 3, 5, 5 )
one or both of those might be incorrect ?

( I'm teasing, perhaps )

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upvoteby inigyou1 hours ago|
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The specification said

    Every item in I is present exactly once in S
5 is an item in I, and it is present exactly once in S.
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upvoteby defrost1 hours ago|
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and 5 is another item in I, and it's not present in S.
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upvoteby inigyou1 hours ago|
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Yes it is, it's right there, between the 4 and the 6.
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upvoteby defrost1 hours ago|
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That's not the same one - track the permutation chain.
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upvoteby Veserv40 minutes ago|
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What is the "same one"? Define item in "I" formally.

Are we talking about Values? Then inigyou is correct.

Memory locations? Then it is trivially true, but that does not prevent me from writing 0 into every memory location.

Value + Memory location? Then it does not work for arrays since we are modifying the memory locations by moving the values between them.

The abstract notion of manipulable things in a indexable order? You need to show how that correlates to reality in a way where you can not put in a hole even larger than this one you are trying to close.

To loop back, this very discussion shows how non-trivial it really is and how much thought actually needs to be put into handling even "trivial" problems. Almost everybody who talks about how we can replace these complex implementations with simpler, understandable specifications has little to no experience with the difficulties of actually creating correct specifications. Anybody who would bring up sorting as "trivial" either has no idea what they are talking about or is so far ahead that they have weird ideas as to what constitutes as "trivial". In both cases, their opinion is highly divorced from practical reality.

That is not to say that it is not worthwhile or even that the specifications are "more complex". It is quite possible the specification is still simpler despite the difficulty, but it is also likely the complex implementation was already totally incomprehensible and a simplified specification is also incomprehensible, it is now just formally incomprehensible.

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