f1:=int(f,z);
delphi1:=simplify(diff(diff(f1,z),z)+4*diff(diff(f1,z1),z2));
f2:=int(int(delphi1,z1),z2)/4;
f:=f1-f2;
test:=simplify(diff(diff(f,z),z)+4*diff(diff(f,z1),z2));