Theorem: nabla^2(x^2 + y^2) - 4 = 0 (quadratic stream-function vorticity)

Theorem (stream-quadratic-vorticity canonical): for the quadratic stream function psi = x^2 + y^2 (cylindrically-symmetric flow), partial_x^2 psi = 2, partial_y^2 psi = 2, so nabla^2 psi = 4 identically. Canonical sympy pins: x_g, y_g =…