Question: can Someone please help me :'(

we were given three questions to do, i got the other two ones out grand but ive been trying to do this for hours and i still don't get it.   it is 

Write a function that produces the power set of a given nite set M, i.e. the set of all subsets.

Thusyour function has

Argument: a finite set M,

Returnvalue: the set of all subsets of M.

Examples: If PP is the procedure,PP({}) returns {{}},PP({a}) returns {{},{a}},PP({a,b}) returns {{},{a},{b},{a,b}},PP({a,b,c}) returns {{},{a},{b},{c},{a,b},{a,c},{b,c},{a,b,c}},PP({a,b,c,d}) returns{{},{a},{b},{c},{d},{a,b},{a,c},{a,d},{b,c},{b,d},{c,d},{a,b,c},{a,b,d},{a,c,d},{b,c,d},{a,b,c,d}}.

you will be rewarded with a lifetime supply of grattitude if you can help me out! thanks.