Question 760761
A = {empty}, {a}, {b}, {c}, {d}
{ab}, {ac}, {ad}, {bc}, {bc}, {cd}
{abc}, {abd}, {acd}, {bcd}
{abcd}


B = {empty}, {4}, {6}, {8}, {9}, {10}
{4, 6}, {4, 8}, {4, 9}, {4, 10}, {6, 8}, {6, 9}, {6, 10}, {8, 9}, {8, 10}, {9, 10}
{4, 6, 8}, {4, 6, 9}, {4, 6, 10}, {4, 8, 9}, {4, 8, 10}, {4, 9, 10}, {6, 8, 9}, {6, 8, 10}, {8, 9, 10}
{4, 6, 8, 9}, {4, 6, 8, 10}, {4, 6, 9, 10}, {4, 8, 9, 10}, {6, 8, 9, 10}
{4, 6, 8, 9, 10}


In general, if a set has n elements, it has 2^n subsets and 2^n - 1 proper subsets.