$
integral.double_(D) v laplace u - u laplace v dif x dif y = integral.cont_(diff D) v (diff u)/(diff bold(n)) - u (diff v)/(diff bold(n)) dif s
$

$
integral.double laplace u dif x dif y = integral.cont (diff u)/(diff bold(n)) dif s
$

$
nabla = bold(e)_r (diff)/(diff r) + bold(e)_theta 1/r (diff)/(diff theta) + 1/(r sin theta) bold(e)_phi (diff)/(diff phi)
$