https://maximummathematics.com/books/foundational-mathematics/logic/satisfiability/index.htmlWe’ve seen plenty of primitive propositions whose truth values are fixed: \[ \begin{array}{ll} \text{Calvin Coolidge was the 30th President of the United States of America.} & \text{(true)} \\ \\ \text{Mitochondria convert ADP into ATP via cellular respiration.} & \text{(true)} \\ \\ \text{Leonardo da Vinci painted the famous ceiling fresco in the Sistine Chapel.} & \text{(false)} \end{array} \]We’ve also seen compound propositions whose truth values depend on the truth values of its atomic propositions.Hugoen-US