  We present a formalization of higher-order logic in the Isabelle proof
assistant, building directly on the foundational framework Isabelle/Pure and
developed to be as small and readable as possible. It should therefore serve as
a good introduction for someone looking into learning about higher-order logic
and proof assistants, without having to study the much more complex
Isabelle/HOL with heavier automation. To showcase our development and approach
we explain a sample proof, describe the axioms and rules of our higher-order
logic, and discuss our experience with teaching the subject in a classroom
setting.
