Restrict an expression twice

Question

I would like to implement such an expression in the UFL language:
$$ \int_{\Gamma} [ < \mathrm{cof} ( D^2 u) > \nabla u ] v \mathrm{dS} $$
However if I write

jump(avg(cofD2u)*grad(u),n)*v*dS

it says "ffc cannot restrict an expression twice". How can I come over this problem?

Comments

Hi, perhaps you can factor it out yourself into something that the compiler can handle. The restricted term in the form can be fit into the identity jump(a*v)=jump(a)*avg(v)+avg(a)*jump(v) with a = avg(u). Then intuitively the doubly restricted terms should behave such that avg(avg(u))=avg(u) and jump(avg(u))=0 and thus jump(avg(u)*v)=avg(u)*jump(v).