#include <cstdio>
#include <utility>
#include <vector>
#include <algorithm>
using namespace std;

#define gcu getchar_unlocked
#define pcu putchar_unlocked
#define _T template <typename T>
#define _HT template <typename H, typename... T>
#define _il inline
#define _in _il int in
#define _sc _il bool scan
_T T in(int c){T n=0;bool m=false;if(c=='-')m=true,c=gcu();
	do{n=10*n+(c-'0'),c=gcu();}while(c>='0');return m?-n:n;} //&&c<='9'
_in() {return in<int>(gcu());}
_T T scan(T &n){int c=gcu();return c==EOF?false:(n=in<T>(c),true);}
_sc(char &c){c=gcu();gcu();return c!=EOF;}
#ifdef _GLIBCXX_STRING
_sc(string &s){int c;s="";
	for(;;){c=gcu();if(c=='\n'||c==' ')return true;else if(c==EOF)return false;s+=c;}}
#endif
_HT _sc(H &h, T&&... t){return scan(h)&&scan(t...);}
#define _vo _il void out
#define _vl _il void outl
_vo(const char *s){while(*s)pcu(*s++);}
_vo(char c){pcu(c);}
#ifdef _GLIBCXX_STRING
_vo(string s){for(char c:s)pcu(c);}
#endif
_T _vo(T n){static char buf[20];char *p=buf;
	if(n<0)pcu('-'),n*=-1;if(!n)*p++='0';else while(n)*p++=n%10+'0',n/=10;
	while (p!=buf)pcu(*--p);}
_vl(){out('\n');}
#ifdef _GLIBCXX_VECTOR
_T _vo(vector<T> &v){for(T &x:v)out(&x == &v[0]?"":" "),out(x);outl();}
#endif
_HT _vo(H&& h, T&&... t){out(h);out(move(t)...);}
template <typename... T> _vl(T&&... t){out(move(t)...);outl();}

void dump(int n) {
		out(n, ':');
		for (int j = 0, t; (t = n >> j); j++)
			if (t & 1)
				out(' ', j);
		outl();
}

typedef vector<int> v;
void enumeration(int t, size_t i, v &k, v &r) {
	if (i >= k.size()) {
		r.push_back(t);
		return;
	}

	enumeration(t, i + 1, k, r);
	enumeration((1 << k[i]) | t, i + 1, k, r);
}

int main() {
	in();
	v k(in()),r;
	for (int &x: k)
		x = in();
	enumeration(0, 0, k, r);
	sort(r.begin(), r.end());
	for (int x: r)
		dump(x);
}
