public void TestParsing20() {
var g = new Grammar(new List<Production>{
CFGParser.Production("<S> → <A> <A>"),
CFGParser.Production("<A> → 'a' <A>"),
CFGParser.Production("<A> → ε")
}, Nonterminal.Of("S"));
var sentences = new List<Sentence>();
sentences.Add(Sentence.FromWords("a"));
ExecuteTest(g, sentences);
}