How to compute first(X) and follow(X)?

• first(B) $\subseteq$ first(A).
• if B is nullable then x $\in$ first(A).
• Naive method: compute first, follow and nullable for right-hand side and from that for A.
• Does not work for recursion!
  
  
• Idea: Start with empty sets and add elements until all conditions are satisfied.
• This is called a fixpoint algorithm (It runs until there are no more changes, until the solution is fix).