This is a formalization of the book "Type Theory and Formal Proof: An Introduction" by Rob Nederpelt and Herman Geuvers.

1. Untyped Lambda Calculus
2. Simply Typed Lambda Calculus ($\lambda ^ \to$)
3. Second-order Typed Lambda Calculus ($\lambda 2$)
4. Types Dependent on Types ($\lambda \underline{\omega}$)

BSD-3-Clause