I completely disagree. Remove-if-not is explicit. You know exactly what it does just by reading it. Your suggestion of filter could either mean use this filter to only grab the the things I want or use this filter to filter out the things I don't want. Complaining about the complexity of a name like "remove-if-not" makes absolutely no sense to me. Anyone can read that name and know exactly what it does. You only know what filter means because of your familiarity with it and not because of any inherit simplicity in its name.