title: FreeFem++: Tangential trace in boundary condition?
body: <p>I want to use Nédélec's elements in FreeFem++ to solve Maxwell's equations in 3D. My problem is that I don't find a way to write the boundary condition which is E × N = F. I tested:</p>
  
  <p><code>on(0, Ehy * N.z - Ehz * N.y = Fx, Ehz * N.x - Ehx * N.z = Fy, Ehx * N.y - Ehy * N.x = Fz)</code></p>
  
  <p>but an error is displayed, and the only thing it says is that there is an error "before token =". If I change the boundary condition to a random one like <code>on(0, Ehx = Fx, Ehy = Fy, Ehz = Fz)</code> it doesn't throw any error so I think the issue comes from the arithmetics operations in the condition.</p>
  
  <p>Any idea?</p>