N:Formula List. 
(nil @ N) = (nil)+(N) 
3. v: Formula List
4.
N:Formula List. (v @ N) = (v)+(N) N:Formula List. ((u.v) @ N) = (u.v)+(N) N:Formula List. (M @ N) = (M)+(N) | 1 | N:Formula List. (nil @ N) = (nil)+(N) |
| 2 | 2. u: Formula 3. v: Formula List 4. N:Formula List. (v @ N) = (v)+(N) N:Formula List. ((u.v) @ N) = (u.v)+(N) |
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