12 lines
693 B
Markdown
12 lines
693 B
Markdown
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---
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tags:
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- Logic
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- propositional-logic
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- derivation-rules
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---
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This rule can seem a little odd: like we are randomly introducing an additional proposition without giving any justification. However this is just a consequence of the fact if $P$ is true, so is $P \lor Q$ since disjunction is not the same as conjunction: only one disjunct needs to be true for the compound disjunction to be true. This is represented in the context of [truth-trees](Truth-trees.md#disjunction-decomposition) by the fact that truth can pass up via either branch of a disjunction pattern.
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This rule is sometimes also referred to (confusingly) as *Addition*.
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