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doc: mention left and right to prove disjunction #899

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2 changes: 1 addition & 1 deletion Manual/BasicProps.lean
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Expand Up @@ -112,7 +112,7 @@ Because {lean}`Sum` is a type, it is possible to check _which_ constructor was u
{lean}`Or`, on the other hand, forms propositions: terms that prove a disjunction cannot be interrogated to check which disjunct was true.
In other words, because {lean}`Or` is not a {tech}[subsingleton], its proofs cannot be used as part of a computation.

In a {ref "tactics"}[tactic] proof, disjunctions can be proved using either constructor ({name}`Or.inl` or {name}`Or.inr`) explicitly via {tactic}`apply`.
In a {ref "tactics"}[tactic] proof, disjunctions can be proved using either constructor ({name}`Or.inl` or {name}`Or.inr`) explicitly via {tactic}`apply`, but {tactic}`left` and {tactic}`right` are more common.
Assumptions of disjunctions in the context can be simplified using {tactic}`cases`, pattern matching with {tactic (show := "match")}`Lean.Parser.Tactic.match`, or {tactic}`rcases`.

{docstring Or}
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