var ESet = ESet || function(json) {
  this.text = json.text || '';           // text contained in the input
  this.symbol = json.symbol || '';       // symbol used for the graph
  this.element = null;                   // DOM element this is tied to
  this.parent = null;                    // Exercise that owns this
  this.entries = json.entries || [];     // Reps (equal to Page's entries
  this.nodes = [];                       // DOM elements, equal to entries
  this.lines = [];                       // DOM elements, equal to entries
};
ESet.prototype.getJSON = function() {
  return {
    text: this.text,
    symbol: this.symbol,
    entries: this.entries
  };
};
ESet.prototype.getNumber = function() {
  return parseInt(this.text);
};