Another classic mis-specification
Postcondition for sorting an array
- ? i,j • i < j ? a[i] <= a[j]
for i := 1 to n do a[i] := i endfor
(? i,j • i < j ? a[i] ? a[j]) ? A = permutation(A’)
- It’s even more complicated if you want to define a stable sorting specification
- Stable sorting leaves equal keys in the same order as they were