code: function(){
  		var opemgr = this.puzzle.opemgr;
  		opemgr.newOperation();
  		opemgr.add(new this.puzzle.klass.BoardClearOperation());
  		
  		this.cell.ansclear();
  		this.cross.ansclear();
  		this.border.ansclear();
  		this.excell.ansclear();
  		opemgr.rejectTrial(true);
  		if(opemgr.history[opemgr.history.length-1].length===1){
  			opemgr.puzzle.undo();
  			opemgr.removeDescendant();
  		}
  		
  		this.rebuildInfo();
  	}
docs: 呼び出し元：回答消去ボタン押した時