Given the following assumptions about the nodes in some kind of trees: VXYy(P(x,y) (N(X)^N(y))) (2.2) Check by resolution that the following formula: (2.2) F ((2.1) X(S(X) N(X))) is a valid formula The formal language is: S(x): x is child node in a tree P(y,x): y is a parent node of the node x N(x): x is a node in a tree