I am trying to write a code on p5.js and cannot figure out why the code below is throwing the error:

Uncaught ReferenceError: RiLexicon is not defined

mySketch, line 18:Cannot read properties of undefined (reading 'isNoun')

I turned on the RiTa.js library but it doesn't work. Hope someone can give an insight.

let poem = "STOPPING BY WOODS ON A SNOWY EVENING WHOSE woods these are I think I know. His house is in the village though; He will not see me stopping here To watch his woods fill up with snow. My little horse must think it queer To stop without a farmhouse near Between the woods and frozen lake The darkest evening of the year. He gives his harness bells a shake To ask if there is some mistake. The only other sound's the sweep Of easy wind and downy flake. The woods are lovely, dark and deep. But I have promises to keep, And miles to go before I sleep, And miles to go before I sleep."

let words;
let newPoem = "";
var lexicon = new RiLexicon();
function setup() {
    createCanvas(windowWidth, windowHeight);
    background(100);
    
    // tokenize the poem string to words
    words = RiTa.tokenize(poem);
    // replace all nouns and adjectives in the text with random nouns and adjectives. 
    // loop through all the words
    for (i=0; i<words.length; i++){
        let currentWord = words[i];
        // when the word is a noun
        if (lexicon.isNoun(currentWord)){
            // generate a new noun and use that as current word
            currentWord = lexicon.randomWord("nn");
        }
        // when the word is an adj
        else if (lexicon.isAdjective(currentWord)){
            // generate a new adj and use that as current word
            currentWord = lexicon.randomWord("jj");
        }
        // add the word to the new poem
        newPoem += currentWord + " ";
    }
    print(newPoem);
}
function draw() {
    textSize(16);
    // display the new poem
    text(newPoem, width/20, height/4, 500, 800);
}