#include <bits/stdc++.h>

#define ll long long

using namespace std;

int solve(){
    int l,r;cin>>l>>r;
    if(l==r)return cout<<-1<<'\n',0;
    if((r-l+1)%2==0){
        for(int i=l;i<=r;i+=2){
            cout<<i + 1<<" "<<i<<' ';
        }
        cout<<'\n';
        return 0;
    }
    if(l%2){
        cout<<l + 1<<" "<<l + 2<<" "<<l<<" ";
        for(int i=l+3;i<=r;i+=2){
            cout<<i+1<<" "<<i<<' ';
        }
        cout<<'\n';
    }else{
        cout<<-1<<'\n';
    }

    return 0;
}

int main(){
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int t=1;
    cin>>t;
    while(t--){
        solve();
    }
    return 0;
}