I'm having trouble understanding a function, in relation to binary rooted trees
Def'n: a binary rooted tree is a tree with a root node in which every node has at most two children.
Def'n: A terminal is a node with no children
Let T be a tree, B the set of all BRTs, n(T) counts the number of nodes in T, z(T) counts the number of terminals
Noting the recursive structure of BRTs, let L be the left subtree, R the right subtree
if either L or R not empty, 1 if both are empty
Thus (this step I don't understand)
I'm having trouble understanding how the function is broken down.