not needed

provided equally on inner and front faces

provided more on inner face than on front face

provided more on front face than on inner face

top face perpendicular to wall

bottom face perpendicular to wall

both top and bottom faces perpendicular to wall

none of the above

(i) and (ii),

(ii) and (iii)

(i) and (iv)

(iii) and (iv)

not provided

provided only on inner face

provided only on front face

provided both on inner and front faces

only (i)

only (ii)

both (i) and (iv)

both (ii) and (iii)