Past exam of the mathematics course of the University of Cambridge / 2024 / ii / Paper 1 / 4J / b / i / Solution

The first displayed tree supplies the productions $S\Rightarrow AS$ and $S\Rightarrow AA$, as well as an $A$-parse tree producing $ab$. By assumption there is also an $A$-parse tree producing $baba$. Substitute these trees as follows:The resulting yield is