Software-bugs are the result of human errors and lack of completeness and logic during the creation-process. It's a fundamental human shortcoming, for which a lasting cure is yet to be found.
Any attempts to correct buggy software without recreating it from scratch, will inevitably lead to even more and more complex bugs finding their way into the software, because of the same human shortcomings.
All software that rely on other software — including Operating Systems (of course), will also rely on its bugs. Thus we get a cascade of bugs from all involved bits of software, which makes even the thought of finding bug-free software completely absurd.
Longer essays may also contain an introductory page that defines words and phrases of the essay's topic. Most academic institutions require that all substantial facts, quotations, and other porting material in an essay be referenced in a bibliography or works cited page at the end of the text. This scholarly convention helps others (whether teachers or fellow scholars) to understand the basis of facts and quotations the author uses to support the essay's argument and helps readers evaluate to what extent the argument is supported by evidence, and to evaluate the quality of that evidence. The academic essay tests the student's ability to present their thoughts in an organized way and is designed to test their intellectual capabilities.