Proof step 1 from proof diff-diff-right (conclusion) (back to tree)

⊦ a ∈ s2 → (a ∈ s0 \ s1 \ s2 ↔ a ∈ s0)

System applied rule normalize

And obtained the following new goals

Proof step 2:
¬(a ∈ s0 \ s1 \ s2 ↔ a ∈ s0), a ∈ s2 ⊦

Rule argument

Additional information

Proof step 2 from proof diff-diff-right (previous step) (back to tree)

¬(a ∈ s0 \ s1 \ s2 ↔ a ∈ s0), a ∈ s2 ⊦

Heuristic simplifier applied rule simplifier

And obtained the following new goals

Proof step 3:
# s2 ≠ 0, ¬(a ∈ s0 \ s1 \ s2 ↔ a ∈ s0), s2 ≠ ∅, a ∈ s2 ⊦

Rule argument

Additional information

Used simplifier rules: size-zero-01: ⊦ s ≠ ∅ → # s ≠ 0; (forward) from specification set-basic ne-01: ⊦ a ∈ s → s ≠ ∅; (forward) from specification set-basic

Proof step 3 from proof diff-diff-right (previous step) (back to tree)

# s2 ≠ 0, ¬(a ∈ s0 \ s1 \ s2 ↔ a ∈ s0), s2 ≠ ∅, a ∈ s2 ⊦

User applied rule apply rewrite lemma

And obtained the following new goals

Proof step 4:
⊦ a ∈ s1 \ s2 ↔ a ∈ s1 ∧ ¬ a ∈ s2

Rule argument

spec: <toplevel>, name:Difference, seq: ⊦ a ∈ s1 \ s2 ↔ a ∈ s1 ∧ ¬ a ∈ s2, subst:[s2, s1, a] → [s1 \ s2, s0, a], <all paths>

Additional information

Used simplifier rules: Difference: ⊦ a ∈ s1 \ s2 ↔ a ∈ s1 ∧ ¬ a ∈ s2; Used terms: s1 \ s2, s0, a

Proof step 4 from proof diff-diff-right (previous step) (back to tree)

⊦ a ∈ s1 \ s2 ↔ a ∈ s1 ∧ ¬ a ∈ s2

Lemma Difference

Proof Tree for diff-diff-right (View conclusion)

The following image shows the proof tree of sequent calculus. The proved goal is at the bottom. You can click on the nodes to view additional rules. See here for details on colors in a proof tree.