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Proof step 1 from proof downcase-lower-a (conclusion)

⊦ downcase('a') = 'a'

User applied rule insert rewrite lemma

And obtained the following new goals

Proof step 2:
⊦ ¬(pos('A', sortedchars) ≤ pos(char, sortedchars) ∧ pos(char, sortedchars) ≤ pos('Z', sortedchars)) → downcase(char) = char
Proof step 3:
¬ ¬(pos('A', sortedchars) ≤ pos('a', sortedchars) ∧ pos('a', sortedchars) ≤ pos('Z', sortedchars)) ⊦ downcase('a') = 'a'

Rule argument

spec: inst: name: Char-downcase-no seq: ⊦ ¬ ( pos('A', sortedchars) ≤ pos(char, sortedchars) ∧ pos(char, sortedchars) ≤ pos('Z', sortedchars)) → downcase(char) = char subst: [char] → ['a'] flags: rewrite, current

Additional information

Used terms: 'a'