Another part to check is the list: Ordinary Differential Equations (ODEs) and Partial Differential Equations (PDEs). These are proper nouns as well, so they should not be altered. The synonyms should only be for other words.

"Undergraduate" → beginning

3. "the behavior of" – "Behavior" can be "functioning," "operation," or "performance." "Of" is preposition, maybe replace with "in," "regarding," or "concerning" but that might be overcomplicating. Wait, the instruction says to touch every term with 3 variants. Hmm. "The behavior of" – maybe "the functioning of," "the operation of," "the performance of," but "the" is an article, should I replace it? The user said "every term," so "the" is a term. Wait, but "the" might be tricky. Let me check instructions again. It says "Don't touch proper nouns." So "the" is a determiner, not a proper noun. So maybe replace "the" with "a," "this," or "that"? Wait, but the sentence structure needs to be maintained. Maybe "the" can stay, but the user wants every term. Hmm. Maybe the user is expecting each individual word. Wait, the original example in the user's message: "Rewrite every term with 3 variants as spintax w2. Don't touch proper nouns. Text only." So "every term" refers to each individual word. But the original sentence is "Differential equations are used to model the behavior of electrical circuits." Let me split it into individual terms:

"Differential equations" → mathematical expressions.

First, I need to parse the original text and identify each word that needs to be replaced. Some words might not have three suitable synonyms, so I should look for the most relevant ones. I'll start with the first sentence: "Differential equations are mathematical equations that describe how a quantity changes over time or space."

"Differential Equations" could be "Differentiated Problems", "Rate-Connected Equations", "Derivative-Based Problems"

But the user might consider "Differential equations" as one term, but I think it's safer to split each individual word. However, "Differential equations" is a compound term. The user might want to keep the compound term as is if it's a proper noun. Wait, "Differential equations" isn't a proper noun. So each word can be replaced.

"First-Order Differential Equations"