public static Expression parseExpression(Object _s){
if (_s instanceof ArrayList)
_s = ((ArrayList)_s).get(0);
if (_s instanceof String){
if (((String)_s).startsWith("?"))
return new Variable(new Atom((String)_s));
return new Atom((String)_s);
}
Statement s = (Statement) _s;
String opt = s.operator.toUpperCase();
Expression res=null;