Give the Complete proof of Theorem 5.1 by showing that the yield of every partial derivation tree with root $S$ is a sentential form of $G$.
Theorem 5.1
Let $G = (V, T, S, P )$ be a context-free grammar. Then for every $w ∈ L (G)$, there exists a derivation tree of $G$ whose yield is $w$. Conversely, the yield of any derivation tree is in $L (G)$. Also, if $t_G$ is any partial derivation tree for $G$ whose root is labeled $S$, then the yield of $t_G$ is a sentential form of $G$.
