tìm tập hợp con: B={T;O;A;N}

Các tập hợp con thỏa mãn bài toán là:
\[\begin{array}{l}
{B_1} = \emptyset ;\,\,{B_2} = \left\{ T \right\};\,\,\,{B_3} = \left\{ O \right\};\,\,{B_4} = \left\{ A \right\};\,\,{B_5} = \left\{ N \right\}\\
{B_6} = \left\{ {T;\,\,O} \right\};\,\,{B_7} = \left\{ {T;\,\,A} \right\};\,\,{B_8} = \left\{ {T;\,\,N} \right\};\,\,{B_9} = \left\{ {O;\,\,A} \right\}\\
{B_{10}} = \left\{ {O;\,\,N} \right\};\,\,{B_{11}} = \left\{ {A;\,\,N} \right\};\,\,\,{B_{12}} = \left\{ {T;\,\,O;\,\,A} \right\};\,\,\,{B_{13}} = \left\{ {T;\,\,O;\,\,N} \right\}\\
{B_{14}} = \left\{ {T;\,\,A;\,\,N} \right\};\,\,\,{B_{15}} = \left\{ {O;\,\,A;\,\,N} \right\};\,\,{B_{16}} = \left\{ {T;\,\,O;\,\,A;\,\,N} \right\}.
\end{array}\]