| ⊦ abs-keys(orphans(fs0, ri0)) = abs-keys(orphans(fs, ri)) ↔ orphans(fs0, ri0) = orphans(fs, ri) |
abs-keys(orphans(fs0, ri0)) = abs-keys(orphans(fs, ri)) ⊦ abs-keys(orphans(fs0, ri0)) = abs-keys(orphans(fs, ri)) ↔ orphans(fs0, ri0) = orphans(fs, ri)
Used formulas: abs-keys(orphans(fs0, ri0)) = abs-keys(orphans(fs, ri))