diamond1.lean:11:40-11:45: error: parent field type mismatch, field 'a' from parent 'Baz' has type
  α → α : Type
but is expected to have type
  α : Type
structure Foo : Type → Type
number of parameters: 1
constructor:
Foo.mk : {α : Type} → Bar (α → α) → (Bool → α) → Nat → Foo α
fields:
toBar : Bar (α → α)
c : Bool → α
d : Nat
def f : Nat → Foo Nat :=
fun x => { a := fun y => x + y, b := fun x1 x2 => x1 + x2, c := fun x_1 => x, d := x }
diamond1.lean:27:47-27:52: warning: field 'a' from 'Baz' has already been declared