Notice that setdiff is not symmetric. Further, note that we can calculate the complement of a set A. noted A and defined to be the elements of s that are not in A simply with in the case There have been methods written for intersect, setdiff, subset, and union that the input objects are of class ps. See Section 4.6.3. Note 4.3 When the prob package loads you will notice a message: "The following object s) are masked from package: base intersect, diff. union". The reason for this mes- setd age is that there already exist methods for the functions intersect, setdiff, union in the base package which ships with R. However, these methods were designed for when the arguments are vectors of the mode. Since we are sa spaces which are data frames and lists, it was same to handle those as well. When the necessary to write methods cases function in the prob package is loaded, R recognizes that there are multiple versions of the same cause for search path and acts to shield the new definitions from the existing ones. But there is no base Ilu linnourn tha nroh functions ha been carefully defined to match the usual