pp_using_anonymous_constructor
This attribute, which was implemented in #3640, is applied to the following structures: `Sigma`, `PSigma`, `PProd`, `And`, `Subtype`, and `Fin`. These were given this attribute in Lean 3.
Implements a Lean 3 pretty printer feature. Structures with the `@[pp_using_anonymous_constructor]` attribute pretty using anonymous constructor notation (`⟨x, y, z⟩`) rather than structure instance notation (`{a := x, b := y, c := z}`). [Zulip discussion](https://leanprover.zulipchat.com/#narrow/stream/270676-lean4/topic/.60pp_using_anonymous_constructor.60/near/425705445)