Category "lean"

Proving A → ¬ (¬ A ∧ B) in Lean

I am having a hard time proving A → ¬ (¬ A ∧ B) with the Lean theorem prover. I set it up like this: example : A → ¬ (¬ A ∧ B)

Is Lean 4 lazy or strict?

Lean 4 is a purely functional programming language, but is it lazy (like Haskell) or strict (like Idris) and what are the implications of this? Is there a way t