function prod( a, b )
    print( "\nPRODUCT:" )
    for m = 1, #a do
        for p = 1, #b do
            for n = 1, #a[m] do
                for q = 1, #b[p] do
                    io.write( string.format( "%3d ", a[m][n] * b[p][q] ) )
                end
            end
            print()
        end
    end
end