Euqiry about the interpolation in FreeFEM

Dear all,
I meet some problems on interpolation.
The following is the code:

solve LP(w,v)=

Here w,v are in the same FEM space V1, while Xi is in another FEM space V2.
Now I want to change the second integration to get this formula:
int2d(V1)(dx(u2)*dx(Ph(v*Xi))+dy(u2)*dy(Ph(v*Xi)), where Ph is the interpolation operator in V1 space. Since v and Xi are FEM functions in different FEM spaces, would you please tell me how to implement this formula in code? Thank you so much!