It is important to keep in mind that an allusionis a reference in literature to something that is well known from other literature, science, history, or pop culture. In chapter 9 of Ender's Game, there are two historical allusions, which are the pseudonyms Peter and Valentine give themselves for identities on "the nets."
Peter's pseudonym is Locke, after John Locke, the English philosopher whose confidence in human nature led him to describe what would become key ideals in representative democracy. Valentine, on the other hand, becomes Demosthenes, after the Greek philosopher who is most known for his speeches which led Athens to go to war with Macedonia.
It is important to understand these allusions because they shed light on the difference between the actual characters of Peter and Valentine, and their personalities on the nets. The persona behind each character's pseudonym in this chapter is somewhat ironic, because in real life, Peter is far more malicious, unjust, and power hungry. His choice of name suggests a much more mild temperament and more understanding of regarding the good of the whole rather than pushing for dictatorship at the mercy of individuals. This is ironic because ultimately, Peter seeks power at the mercy of anyone and everyone who is weaker than he is.
Meanwhile, Valentine's persona (the sibling who did not get chosen for Battle School because she was too mild mannered and a peace-maker) suggests someone who is more ruthless, and seeking to stir up descent in those not in leadership to overthrow those in power.
Because Valentine and Peter are writing from perspectives that go against their natures, they must rely on one another for ideas and to make sure that what they are discussing sounds realistic.