improper definition in lammps

hi all
i have a problem with improper definition to lammps .I have a improper between i,j,k and l atoms (atom l moves out of plane). how can I define it to the lammps? I mean the order of atoms for definition (i, j ,k , l ) or (j, i, k , l) or ( i , k , j ,l) or something else.
thanks dear friends

I believe impropers are specified as i l j k (the atom moving out of plane is the second position).