To start proving a theorem, give the New Theorem command. A dialog box will open, asking you to enter the hypotheses and conclusion of the theorem you want to prove. To enter a hypothesis, type it into the space labeled “Enter hypotheses and conclusion here” and then click the Add Hypothesis button, and it will be added to the list of hypotheses. To enter the conclusion, type it in and click the Set Conclusion button. When typing the hypotheses and conclusion, use ordinary set-theoretic and logical notation. (For a more complete explanation of how to type statements into Proof Designer, click here.) If you change your mind about one of the hypotheses, you can click on it to select it and then click the Cut Hypothesis button to remove it from the list. If you change your mind about the conclusion, just type in a different conclusion and click the Set Conclusion button. The new conclusion will replace the old one. When you have entered the hypotheses and conclusion, click OK. The theorem will be entered into the Proof Designer window, and you can begin working on constructing the proof.
Note that if you are in the middle of proving a theorem when you use the New Theorem command, the theorem you are working on will be discarded and replaced by the new theorem you enter. So if you don't want to lose the proof you are working on, use the Save command to save it before using the New Theorem command.