This rule is used to introduce an OR formula into a proof by using an existing formula in the proof as one side of the OR formula and a formula the user enters for the other side. (the user must enter a formula that uses only relation symbols, function symbols or constants that are in the signature of the box you are working in), or when used backwards to extract a sub formula of an OR formula to use as a goal.

1. select both an empty line and click on Or Introduction.
2. then select the line containing the formula you wish to use as one side of the OR formula (this line must be in scope of the empty line).
3. choose when asked the side of the OR statement you want the selected formula to appear on left or right.
4. next enter the formula you wish to appear on the other side of the OR formula.
5. the OR formula will be added as a new line to your proof

1. select both the goal line in your proof or box (this line must be an OR formula) and Or Introduction.
2. when prompted choose the side of the formula you wish to extract as your new goal.
3. the sub formula will appear as a new goal line.