If you're having trouble applying either &EL or &ER, click on the statement below that best describes the problem you're having.
I can't select &EL/&ER from the Elim Rules menu.
If a rule is not appearing in the ToolBox menus, then that rule is not available for the currently loaded problem. Rules are available only for derivation problems that follow the presentation of the rule in the text, regardless of what problems you may have completed previously.
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I can't select the conjunction I want to eliminate in the Fitch.
First, make sure that there isn't a problem with your mouse by clicking to change applications or browser windows. If your mouse is working properly, try clicking on different parts of the formula. If you are still unable to select the formula no matter where you click on it, try exiting the CPL and reloading the problem. If the problem persists after reloading, please inform your instructor.
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When I clicked the Apply Rule button, I got an error message that said the formula I had selected was not a conjunction.
Conjunction elimination can only be applied to conjunctions. Check carefully to make certain that the formula you are selecting really is a conjunction. Any conjunction will appear in the Fitch in the form ( φ & ψ ).
If the formula is definitely a conjunction but you still get the same error message when applying the rule, try exiting the CPL and then reloading the problem. If the problem persists after reloading, please inform your instructor.
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When I clicked the Apply Rule button, I got another error message or nothing happens.
Make sure that you have selected the correct rule in the ToolBox, and that you have selected a conjunction in the Fitch. If your selections are correct, the formula that will be derived when the rule is applied will auto-fill in the instantiation pane of the ToolBox.
If the formula is auto-filled, but you continue to experience problems when attempting to apply the rule, try exiting the CPL and reloading the problem. If the problems persist after reloading, please inform your instructor.
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I'm trying to apply &EL/&ER backwards.
Elimination rules can't be applied backwards in the CPL.
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I'm trying to apply &EL/&ER to more than one line.
Conjunction elimination is applied to only a single line, and the formula on that line must be a conjunction.
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I can apply the rule successfully, but the wrong conjunct is derived.
You probably just selected the wrong variant of the rule by mistake. Check the justification for the new line in the Fitch, and if the rule applied was &EL, select &ER and reapply to the same conjunction, or if the rule was &ER, select &EL and reapply.
Show me where to look for the justification
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