First, I need to identify the words that are not proper nouns. Proper nouns are names of specific people, places, organizations, etc., like "Alice" or "New York." So I have to make sure those stay the same.

- For each word, check if it's a proper noun (maybe by capitalization). - If not, generate three variants. - Replace accordingly.

Also, some words are part of fixed phrases. For example, "set up a meeting" – replacing "set" might not make sense unless the context is right. But without knowing context, it's hard to preserve meaning.

But since in this case, the user is just setting up the task, I need to confirm that I understand the requirements. Let me summarize:

Another consideration: words that might be part of a compound word, like "mother-in-law." But in the input text, they might be written with hyphens or as separate words. Not sure how to handle that. The instruction is to not change proper nouns, so if "mother-in-law" is part of a proper noun, like "Jane Smith, Mrs. John mother-in-law," but probably not. Unless the system can't tell, just proceed word by word.

But how to generate three synonyms? For that, I need a thesaurus. However, since I don't have access to external resources, I have to rely on my internal knowledge. So for each word, think of three synonyms. If I can't, maybe use different forms or related terms.

Processed output: "This speedy tan animal hops across the lethargic dog, yet Alice remains calm."

Also, punctuation. Are words separated by spaces part of the same token? For example, "New York" is a proper noun and should remain as is. But if it's written as separate words, like "new york," then maybe they would be changed if not part of a proper noun. Wait, but proper nouns have to be capitalized? So maybe the system can check for capitalization. But not always reliable because sometimes words might be in the middle of a sentence and still be part of a proper noun.