c.find({a: {$gte: 20}}, {sort: {a: 1, b: -1}, skip: 50, limit: 5}).fetch(), [
      {a: 45, b: 1, _id: '45_1'},
      {a: 45, b: 0, _id: '45_0'},
      {a: 46, b: 1, _id: '46_1'},
      {a: 46, b: 0, _id: '46_0'},