| ⊦ ¬ a ∈ s ∪ s0 ∧ s1 ⊆ s → ¬ a ∈ (s1 -- b) ∪ s0 |
a ∈ (s1 -- b) ∪ s0, s1 ⊆ s, ¬ a ∈ s ∪ s0 ⊦
| a ∈ (s1 -- b) ∪ s0, s1 ⊆ s, ¬ a ∈ s ∪ s0 ⊦ |
Used simplifier rules: unrax: ⊦ a ∈ s ∪ s0 ↔ a ∈ s ∨ a ∈ s0; Delete: ⊦ a ∈ s -- b ↔ a ≠ b ∧ a ∈ s; ne-01: ⊦ a ∈ s → s ≠ ∅; (forward) from specification polyinfset-basic sub-in: ⊦ a ∈ s ∧ s ⊆ s0 → a ∈ s0; (forward) from specification polyinfset-basic
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.