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[doc] improve Eql precise rules + typo and format #7197

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Sep 11, 2019
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[doc] improve Eql precise rules + typo and format #7197

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15 changes: 6 additions & 9 deletions docs/docs/reference/contextual/multiversal-equality.md
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Expand Up @@ -112,24 +112,21 @@ The precise rules for equality checking are as follows.

If the `strictEquality` feature is enabled then
a comparison using `x == y` or `x != y` between values `x: T` and `y: U`
is legal if

1. there is a given instance for `Eql[T, U]`, or
2. one of `T`, `U` is `Null`.
is legal if there is a given instance for `Eql[T, U]`.

In the default case where the `strictEquality` feature is not enabled the comparison is
also legal if

1. `T` and `U` the same, or
2. one of `T` and `U`is a subtype of the _lifted_ version of the other type, or
3. neither `T` nor `U` have a _reflexive `Eql` given.
1. `T` and `U` are the same, or
2. one of `T`, `U` is a subtype of the _lifted_ version of the other type, or
3. neither `T` nor `U` have a _reflexive_ `Eql` given.

Explanations:

- _lifting_ a type `S` means replacing all references to abstract types
in covariant positions of `S` by their upper bound, and to replacing
all refinement types in covariant positions of `S` by their parent.
- a type `T` has a _reflexive `Eql` given if the implicit search for `Eql[T, T]`
- a type `T` has a _reflexive_ `Eql` given if the implicit search for `Eql[T, T]`
succeeds.

## Predefined Eql Instances
Expand All @@ -139,7 +136,7 @@ The `Eql` object defines givens for comparing
- `java.lang.Number`, `java.lang.Boolean`, and `java.lang.Character`,
- `scala.collection.Seq`, and `scala.collection.Set`.

Given instances are defined so that every one of these types has a reflexive `Eql` given, and the following holds:
Given instances are defined so that every one of these types has a _reflexive_ `Eql` given, and the following holds:

- Primitive numeric types can be compared with each other.
- Primitive numeric types can be compared with subtypes of `java.lang.Number` (and _vice versa_).
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