Soloviev: Δ*ψ=R²(A+B); ψ(R₀,0)=0; ∂ψ/∂R|(R₀,0)=0; closed-form tokamak eq

Sympy-exact symbolic witness of Soloviev's analytic tokamak equilibrium. Setup: R, R₀, Z, A, B sp-symbols positive; ψ_Sol = A·(R²-R₀²)²/8 + B·R²·Z²/2. Grad-Shafranov operator applied to ψ_Sol yields Δ*ψ = ∂²ψ/∂R² - (1/R)·∂ψ/∂R + ∂²ψ/∂Z²…