HumanEval/16

[TwoFX]

This issue tracks the progress of our solution of HumanEval16.

[TwoFX]

Something like

theorem foo {s : String} {c : Char} :
    count_distinct_characters (s.push c) = if c ∈ s.toList then count_distinct_characters s else count_distinct_characters s + 1 := sorry