A_i	B₁	B₂	$\dots$	B_k
B₁	b₁₁	b₁₂	$\dots$	b_1k
B₂	b₂₁	b₂₂	$\dots$	b_2k
$⋮$	$⋮$	$⋮$	$⋮$	$⋮$
B_k	b_k₁	b_k₂	$\dots$	b_kk