mkIPOcc = mk_simple_deriv varName "$i"
mkSpecOcc = mk_simple_deriv varName "$s"
mkForeignExportOcc = mk_simple_deriv varName "$f"
mkIPOcc = mk_simple_deriv varName "$i"
mkSpecOcc = mk_simple_deriv varName "$s"
mkForeignExportOcc = mk_simple_deriv varName "$f"