| ok(nf(n0)), ok(nf(0)), rel(nf(n0), elemf(nf(n0))), ok(elemf(nf(n0))), ∀ b. ok(b) → rel(b, elemf(b)) ∧ ok(elemf(b)), ∀ m. m < n0 → ok(nf(m)) ∧ nf(m + 1) = elemf(nf(m)) ⊦ ok((n0 + 1 = m ⊃ elemf(nf(n0));nf(m))), n0 < m |
n0 + 1 ≠ m, ok(nf(n0)), ok(nf(0)), rel(nf(n0), elemf(nf(n0))), ok(elemf(nf(n0))), ∀ b. ok(b) → rel(b, elemf(b)) ∧ ok(elemf(b)), ∀ m. m < n0 → ok(nf(m)) ∧ nf(m + 1) = elemf(nf(m)) ⊦ ok(nf(m)), n0 < m