| 1 | 13. s1 = (s1@0 @ e) 14. ([inl(i)] @ s2@0) = (e @ s2) 15. e1: (T+T) List 16. [inl(i)] = (e @ e1) & s2 = (e1 @ s2@0) | 7 steps |
|   | ||
| 2 | 13. s1 = (s1@0 @ e) 14. ([inl(i)] @ s2@0) = (e @ s2) 15. e1: (T+T) List 16. e = ([inl(i)] @ e1) & s2@0 = (e1 @ s2) | 4 steps |
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