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This rule can be used forwards to derive a negated formula or backwards on a not goal line by opening a box which assumes the complement of the goal
line and has a conclusion of bottom.
To use it forwards:
- select the empty line and Not Introduction.
- then enter the negated formula you wish to derive when prompted. This formula must not contain any predicate symbols,
function symbols or constants that are not in the signature of the box you are working in.
- a new box is added to your proof to prove the negated formula you wish to insert with the assumption the complement of the goal line and the
conclusion bottom.
To use it backwards:
- select both the goal line, which must be a NOT formula, and Not Introduction.
- this will add a new box to your proof with the assumption the complement of the goal line and the conclusion bottom.
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