[
A =
begin{bmatrix}
B & C
end{bmatrix}
=
begin{bmatrix}
D & E \
F & G
end{bmatrix}
]

[
A =
left [
begin{array}[t]{cc}
B & C
end{array}
right ]
=
left [
begin{array}[t]{cc}
D & E \
F & G
end{array}
right ]
]