Hi (-), Can one in Firedrake split a volume integration in 3D, in a horizontal part (dx dy) and a vertical part (dz), as follows: \int_x\int_y f(x,y,t) [ \int_z g(x,y,z,) dz ] dy dx instead of \iiint f(x,y,t) g(x,y,z,t) dx dy dz ? Best wishes, Onno