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chore: discuss alternative calc syntax in RELEASES.md

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Adrien Champion 2023-02-24 16:30:43 +01:00 • committed by Sebastian Ullrich
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RELEASES.md
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@ -1,6 +1,31 @@
Unreleased
---------
* [make `calc` require the sequence of relation/proof-s to have the same indentation](https://github.com/leanprover/lean4/pull/1844),
and [add `calc` alternative syntax allowing underscores `_` in the first relation](https://github.com/leanprover/lean4/pull/1844)
the flexible indentation in `calc` was often used to align relations/proofs
```lean
example (x y : Nat) : (x + y) * (x + y) = x * x + y * x + x * y + y * y :=
calc
(x + y) * (x + y) = (x + y) * x + (x + y) * y := by rw [Nat.mul_add]
-- improper indentation
_ = x * x + y * x + (x + y) * y := by rw [Nat.add_mul]
_ = x * x + y * x + (x * y + y * y) := by rw [Nat.add_mul]
_ = x * x + y * x + x * y + y * y := by rw [←Nat.add_assoc]
```
this is no longer legal, but the alternative syntax accomplishes essentially the same goal with proper indentation:
```lean
example (x y : Nat) : (x + y) * (x + y) = x * x + y * x + x * y + y * y :=
calc (x + y) * (x + y)
_ = (x + y) * x + (x + y) * y := by rw [Nat.mul_add]
_ = x * x + y * x + (x + y) * y := by rw [Nat.add_mul]
_ = x * x + y * x + (x * y + y * y) := by rw [Nat.add_mul]
_ = x * x + y * x + x * y + y * y := by rw [←Nat.add_assoc]
```
* Update Lake to latest prerelease.
* [Make go-to-definition on a typeclass projection application go to the instance(s)](https://github.com/leanprover/lean4/pull/1767).