1. v : ℝ
2. v = (π/r(4))
3. MachinPi4() = v ∈ {x:ℝ| x = (π/r(4))}
⊢ (r(2) * v) = π/2
{ (RWO "-2" 0 THEN Auto) }
⊢ (r(2) * (π/r(4))) = π/2