Little Alchemy(littlealchemy.com)

  function combRep(arr, l) {
    if (l === void 0) l = arr.length; // Length of the combinations
    var data = Array(l), // Used to store state
        results = [
        ]; // Array of results
    (function f(pos, start) { // Recursive function
      if (pos === l) { // End reached
        results.push(data.slice()); // Add a copy of data to results
        return;
      }
      for (var i = start; i < arr.length; ++i) {
        data[pos] = arr[i]; // Update data
        f(pos + 1, i); // Call f recursively
      }
    }) (0, 0); // Start at index 0
    return results; // Return results
  }
  var parents = [];
  for(b in bases.base) {
    if (bases.base[b].parents != undefined) {
      for (p of bases.base[b].parents) {
        parents[p.sort().join('-')] = b;
      }
    }
  }

  function gethints() {
    combinations = combRep([1, 2, 3, 4].concat(game.progress), 2);
    for (c of combinations) {
      let idx = c.sort().join('-');
      if (parents[idx] != undefined && game.progress.find((e, i, a) => parents[idx] == e) == undefined) {
        console.log(bases.names[c[0]], bases.names[c[1]]);      
      }
    }
  }