Thanks, Paolo! It is not exactly what I need - I am solving a vector eigenvalue problem for elasticity, see FreeFem manual and want to impose mixed boundary conditions: tangential component of traction to vanish (which is automatic due to the weak formulation), and the normal component of the vector field [u,v], that is u*N.x+v*N.y to vanish as well. It’s the second one I’m struggling with.
M.