bonjour je me demande s'il n'y a pas une erreur de transcription : est ce que ça ne serait pas : "il sait celui qui s'efface"?

In fact, "S" means "se", wich we use for the the third person of the pronominal verbs, like "se lever" (to get up) for example. We use pronominal verbs in three cases : reflexivity, reciprocity or for idiomatic reason. This pronoun chenges depending on the person which is used with. It can be one of (me,te,"SE",nous,vous). Example : - Je me lève - Tu te lève - Il/Elle se lève - Nous nous levons - Vous vous levez -Ils/Elles se lèvent (the verb : se lever). Another example, when i say : "je me lave" (verb : to wash), it means like i am saying (i wash my-self) When we have a verb that starts with a voyel as those you have given in your question, we use only : m' ,t' , s' (when nous/ vous don't change). It's like "CI" in italian when we say (ci vediamo) for example.