univInference.lean:25:48-25:54: error: Resulting type is of the form
  Type ?u
but the universes of constructor arguments suggest that this could accidentally be a higher universe than necessary. Explicitly providing a resulting type will silence this error. Universe inference suggests using
  Sort (max (max 1 u) v)
if the resulting universe level should be at the above universe level or higher.

Explanation: At this point in elaboration, universe level unification has committed to using a resulting universe level of the form `?u+1`. Constructor argument universe levels must be no greater than the resulting universe level, and this condition implies the following constraint(s):
  u ≤ ?u+1
  v ≤ ?u+1
However, such constraint(s) usually indicate that the resulting universe level should have been in a different form. For example, if the resulting type is of the form `Sort (_ + 1)` and a constructor argument is in universe `Sort u`, then universe inference would yield `Sort (u + 1)`, but the resulting type `Sort (max 1 u)` would avoid being in a higher universe than necessary.
S6 : Sort (max w₁ w₂) → Type w₂ → Sort (max w₁ (w₂ + 1))
univInference.lean:45:48-45:62: error: Invalid universe polymorphic resulting type: The resulting universe is not `Prop`, but it may be `Prop` for some parameter values:
  Sort (max u v)

Hint: A possible solution is to use levels of the form `max 1 _` or `_ + 1` to ensure the universe is of the form `Type _`
univInference.lean:64:48-64:54: error: Resulting type is of the form
  Type ?u
but the universes of constructor arguments suggest that this could accidentally be a higher universe than necessary. Explicitly providing a resulting type will silence this error. Universe inference suggests using
  Sort (max (max 1 u) v)
if the resulting universe level should be at the above universe level or higher.

Explanation: At this point in elaboration, universe level unification has committed to using a resulting universe level of the form `?u+1`. Constructor argument universe levels must be no greater than the resulting universe level, and this condition implies the following constraint(s):
  u ≤ ?u+1
  v ≤ ?u+1
However, such constraint(s) usually indicate that the resulting universe level should have been in a different form. For example, if the resulting type is of the form `Sort (_ + 1)` and a constructor argument is in universe `Sort u`, then universe inference would yield `Sort (u + 1)`, but the resulting type `Sort (max 1 u)` would avoid being in a higher universe than necessary.
univInference.lean:73:48-73:62: error: Invalid universe polymorphic resulting type: The resulting universe is not `Prop`, but it may be `Prop` for some parameter values:
  Sort (max u v)

Hint: A possible solution is to use levels of the form `max 1 _` or `_ + 1` to ensure the universe is of the form `Type _`
univInference.lean:81:48-81:62: error: Invalid universe polymorphic resulting type: The resulting universe is not `Prop`, but it may be `Prop` for some parameter values:
  Sort (max u v)

Hint: A possible solution is to use levels of the form `max 1 _` or `_ + 1` to ensure the universe is of the form `Type _`