#include <bits/stdc++.h>
using namespace std;
long long pwr(long long base, long long p, long long mod) {
  long long ans = 1;
  while (p) {
    if (p & 1) ans = (ans * base) % mod;
    base = (base * base) % mod;
    p /= 2;
  }
  return ans;
}
long long gcd(long long a, long long b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
int indeg[3 * 100005];
int tree[5 * 300005][2];
vector<int> v[300005];
vector<pair<int, int> > edge;
void build_tree(int node, int a, int b) {
  if (a > b) return;
  if (a == b) {
    tree[node][0] = indeg[a];
    tree[node][1] = a;
    return;
  }
  build_tree(node * 2, a, (a + b) / 2);
  build_tree(node * 2 + 1, 1 + (a + b) / 2, b);
  tree[node][0] = min(tree[node * 2][0], tree[node * 2 + 1][0]);
  if (tree[node][0] == tree[node * 2][0]) {
    tree[node][1] = tree[node * 2][1];
  } else {
    tree[node][1] = tree[node * 2 + 1][1];
  }
}
void update(int node, int a, int b, int idx, int val) {
  if (a == b) {
    indeg[idx] = val;
    tree[node][0] = val;
    tree[node][1] = idx;
  } else {
    int mid = (a + b) / 2;
    if (a <= idx && idx <= mid) {
      update(2 * node, a, mid, idx, val);
    } else {
      update(2 * node + 1, mid + 1, b, idx, val);
    }
    tree[node][0] = min(tree[2 * node][0], tree[2 * node + 1][0]);
    if (tree[node][0] == tree[node * 2][0]) {
      tree[node][1] = tree[node * 2][1];
    } else {
      tree[node][1] = tree[node * 2 + 1][1];
    }
  }
}
pair<int, int> query_tree(int node, int a, int b, int i, int j) {
  if (a > b || a > j || b < i) return {1000000, -1};
  if (a >= i && b <= j) {
    pair<int, int> vv = {tree[node][0], tree[node][1]};
    return vv;
  }
  pair<int, int> q1 = query_tree(node * 2, a, (a + b) / 2, i, j);
  pair<int, int> q2 = query_tree(1 + node * 2, 1 + (a + b) / 2, b, i, j);
  pair<int, int> res;
  if (q1.first < q2.first) {
    res = q1;
  } else {
    res = q2;
  }
  return res;
}
int main() {
  int t, n, m, a, b;
  vector<int> ans;
  cin >> t;
  while (t--) {
    cin >> n >> m;
    for (int i = 0; i <= 3 * n; i++) {
      v[i].clear();
      indeg[i] = 0;
    }
    edge.clear();
    for (int i = 0; i < m; i++) {
      cin >> a >> b;
      indeg[a]++;
      v[a].push_back(b);
      v[b].push_back(a);
      indeg[b]++;
      edge.push_back({a, b});
    }
    build_tree(1, 1, 3 * n);
    ans.clear();
    pair<int, int> ttt;
    for (int i = 0; i < n; i++) {
      ttt = query_tree(1, 1, 3 * n, 1, 3 * n);
      if (ttt.first >= 1000000) {
        break;
      }
      ans.push_back(ttt.second);
      update(1, 1, 3 * n, ttt.second, (int)1000000);
      for (int j = 0; j < v[ttt.second].size(); j++) {
        update(1, 1, 3 * n, v[ttt.second][j], (int)1000000);
      }
    }
    if (ans.size() >= n) {
      cout << "IndSet" << endl;
      for (int i = 0; i < ans.size(); i++) {
        cout << ans[i] << " ";
      }
      cout << endl;
    } else {
      for (int i = 0; i <= 3 * n; i++) {
        indeg[i] = 0;
      }
      ans.clear();
      for (int i = 0; i < m; i++) {
        if (indeg[edge[i].first] == 0 && indeg[edge[i].second] == 0) {
          ans.push_back(i + 1);
          indeg[edge[i].first] = 1;
          indeg[edge[i].second] = 1;
        }
      }
      if (ans.size() >= n) {
        cout << "Matching" << endl;
        for (int i = 0; i < n; i++) {
          cout << ans[i] << " ";
        }
        cout << endl;
      } else {
        cout << "Impossible" << endl;
      }
    }
  }
}
