| p ∈ tree ⊦ (tree -- p).fids = tree.fids \ tree[p].fids, p = ε |
str + p0 ∈ tree, ∀ tree. p0 ∈ tree → (tree -- p0).fids = tree.fids \ tree[p0].fids ∨ p0 = ε ⊦ str + p0 = ε, (tree -- (str + p0)).fids = tree.fids \ tree[str + p0].fids
Used simplifier rules: path freely generated by ε, +;;