#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace std;
using namespace __gnu_pbds;
typedef tree<int, null_type, less<int>, rb_tree_tag,tree_order_statistics_node_update> ordered_set;

#define scan(x) do{while((x=getchar())<'0'); for(x-='0'; '0'<=(_=getchar()); x=(x<<3)+(x<<1)+_-'0');}while(0)
char _;
#define complete_unique(a) a.erase(unique(a.begin(),a.end()),a.end())
#define all(a) a.begin(),a.end()
#define println printf("\n");
#define readln(x) getline(cin,x);
#define pb push_back
#define endl "\n"
#define INT_INF 0x3f3f3f3f
#define LL_INF 0x3f3f3f3f3f3f3f3f
#define MOD 1000000007
#define mp make_pair
#define fastio cin.tie(0); cin.sync_with_stdio(0);

#define MAXN 300005
#define MAXM 500005

typedef unsigned long long ull;
typedef long long ll;
typedef long double ld;
typedef unordered_map<int,int> umii;
typedef pair<int,int> pii;
typedef pair<double,double> pdd;
typedef pair<ll,ll> pll;
typedef pair<int,pii> triple;
typedef int8_t byte;

mt19937 g1(time(0));

int randint(int a, int b){return uniform_int_distribution<int>(a, b)(g1);}
ll randlong(ll a,ll b){return uniform_int_distribution<long long>(a, b)(g1);}

ll gcd(ll a, ll b){return b == 0 ? a : gcd(b, a % b);}
ll lcm(ll a, ll b){return a*b/gcd(a,b);}
ll fpow(ll  b, ll exp, ll mod){if(exp == 0) return 1;ll t = fpow(b,exp/2,mod);if(exp&1) return t*t%mod*b%mod;return t*t%mod;}
ll divmod(ll i, ll j, ll mod){i%=mod,j%=mod;return i*fpow(j,mod-2,mod)%mod;}

int num_cases,num_nodes,N,M,deg[MAXN];
bool bad[MAXN];
vector<pii> connections[MAXN];
set<pair<int,pair<pii,int>>> edges; //sum,a,b,idx
vector<pii> oe;
set<pii> s;

int main(){
	scanf("%d",&num_cases);
	while(num_cases--){
		scanf(" %d %d",&N,&M);
		for(int i=1; i<=3*N; i++){
			connections[i].clear();
			deg[i] = 0;
			bad[i] = false;
		}
		edges.clear();
		oe.clear();
		s.clear();

		for(int i=0; i<M; i++){
			int a,b; scanf(" %d %d",&a,&b);
			connections[a].pb(mp(b,i));
			connections[b].pb(mp(a,i));
			oe.pb(mp(a,b));
			deg[a]++, deg[b]++;
		}
		num_nodes = N*3;
		for(int i=1; i<=num_nodes; i++)
			s.insert(mp(deg[i],i));
		bool node_one = true;
		vector<int> res;
		for(int q=0; q<N; q++){
			if(!s.size()){
				node_one = false;
				break;
			}
			pii tk = *s.begin(); s.erase(s.begin());
			res.pb(tk.second);
			for(pii check:connections[tk.second]){
				s.erase(mp(deg[check.first],check.first));
				bad[check.first] = true;
			}
//			for(pii c1:connections[tk.second]){
//				for(pii c2:connections[c1.first]){
//					if(c2.first == tk.second || bad[c2.first]) continue;
//					s.erase(mp(deg[c2.first],c2.first));
//					deg[c2.first]--;
//					s.insert(mp(deg[c2.first],c2.first));
//				}
//			}
		}
		if(node_one){
			printf("IndSet\n");
			for(int check:res)
				printf("%d ",check);
			printf("\n");
			continue;
		}
		bool edge_one = true;
		for(int i=1; i<=num_nodes; i++)
			deg[i] = (int)connections[i].size();
		for(int i=0; i<oe.size(); i++){
			pii check = oe[i];
			int a = check.first, b = check.second;
			if(a > b) swap(a,b);
			edges.insert(mp(deg[a]+deg[b],mp(mp(a,b),i)));
		}
		res.clear();
		for(int q=0; q<N; q++){
			if(!edges.size()){
				edge_one = false;
				break;
			}
			auto tk = *edges.begin(); edges.erase(edges.begin());
			res.pb(tk.second.second);
			int a = tk.second.first.first, b = tk.second.first.second;
			for(pii check:connections[a]){
				if(check.first == b) continue;
				int sum = deg[a]+deg[check.first];
				int aa = min(a,check.first), bb = max(a,check.first);
				pair<int,pair<pii,int>> p = mp(sum,mp(mp(aa,bb),check.second));
				edges.erase(p);
			}
			for(pii check:connections[b]){
				if(check.first == a) continue;
				int sum = deg[a]+deg[check.first];
				int aa = min(b,check.first), bb = max(b,check.first);
				pair<int,pair<pii,int>> p = mp(sum,mp(mp(aa,bb),check.second));
				edges.erase(p);
			}
		}
		if(edge_one){
			printf("Matching\n");
			for(int check:res)
				printf("%d ",check+1);
			printf("\n");
			continue;
		}
		printf("Impossible\n");
	}
}
/*
1
2 5
1 2
3 1
1 4
5 1
1 6

 */