public override string ToString() {
StringBuilder sb = new StringBuilder("Deletion(");
sb.Append("Timestamp: ");
sb.Append(Timestamp);
sb.Append(",Super_column: ");
sb.Append(Super_column);
sb.Append(",Predicate: ");
sb.Append(Predicate== null ? "<null>" : Predicate.ToString());
sb.Append(")");
return sb.ToString();
}