It is not possible to simply assert something in a scientific text; all our statements must have a basis. Either a reason must be given for our statement or we must demonstrate that someone made (and thus somehow justified) this statement before us. References are used for this second purpose – the name or names of the authors of the relevant source and the year of the publication are written directly in the text and a list of references is placed at the end of the text, giving the name of the relevant article and journal or book where it was published. Understandably, it would be best to give the author who discovered the fact or was the first to give a basis for it. However, in practice this is usually far from the case. Authors of articles usually cite the sources from which they themselves learned the given fact. Of course, at least theoretically it should be possible to follow the chain of references in older and older journals back to the original source. Scientific workers are glad when they are cited in the works of other authors. The purpose of a number of citations in scientific articles is thus to please (or corrupt) the relevant colleagues, who could well be amongst the reviewers of the particular article and thus decide on its acceptance for publication (see Review process in a scientific journal) or, at the very least, in the future can, in return, cite our articles in their works.