#include <bits/stdc++.h>
using namespace std;

#define f first
#define s second
#define pb push_back
#define ar array
#define all(x) x.begin(), x.end()
#define siz(x) (int)x.size()

#define FOR(x, y, z) for(int x = (y); x < (z); x++)
#define ROF(x, z, y) for(int x = (y-1); x >= (z); x--)
#define F0R(x, z) FOR(x, 0, z)
#define R0F(x, z) ROF(x, 0, z)
#define trav(x, y) for(auto&x:y)

using ll = long long;
using vi = vector<int>;
using vl = vector<long long>;
using pii = pair<int, int>;
using vpii = vector<pair<int, int>>;

template<class T> inline bool ckmin(T&a, T b) {return b < a ? a = b, 1 : 0;}
template<class T> inline bool ckmax(T&a, T b) {return b > a ? a = b, 1 : 0;}
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

const char nl = '\n';
const int mxN = 2e5 + 10;
const int MOD = 1e9 + 7;
const long long infLL = 1e18;

void solve(){
    int n, k;
    cin >> n >> k;
    k -= n-1;
    if(k>n*(n-1)/2||k<0){
        cout << "IMPOSSIBLE\n";
        return;
    }
    vi a(n, -1);
    F0R(i, n){
        if(k>n-i-1){
            if(i%2==0){
                a[n-(i/2)-1] = i;
            }
            else{
                a[i/2] = i;
            }
            k -= n-i-1;
        }
        else{
            if(i%2==0){
                a[n-(i/2)-1-((n-i-1)-k)] = i;
            }
            else{
                a[i/2+((n-i-1)-k)] = i;
            }
            int cnt = i+1;
            int SP = -1;
            bool seen = 0;
            if(i%2==0){
                F0R(j, n){
                    if(a[j]!=-1&&!seen) SP = j;
                    if(a[j]==-1) a[j] = cnt++, seen = 1;
                }
                reverse(a.begin()+SP+1, a.begin()+n-(i/2)-1-((n-i-1)-k));
            }
            else{
                SP = n;
                R0F(j, n){
                    if(a[j]!=-1&&!seen) SP=j;
                    if(a[j]==-1) a[j] = cnt++, seen = 1;
                }
                reverse(a.begin()+i/2+((n-i-1)-k)+1, a.begin()+SP);
            }
            k = 0;

            break;
        }
    }
    F0R(i, n){
        cout << a[i]+1 <<  ' ';
    }
    cout << nl;
}

int32_t main(){
    ios_base::sync_with_stdio(0); cin.tie(0);
    int t; cin >> t;
    F0R(i, t){
        cout << "Case #" << i+1 << ": ";
        solve();
    }

    return 0;
}