This lecture covers inductive propositions and reasoning, focusing on their definitions and applications in Coq. The instructor begins by revisiting inductive types, emphasizing their importance in constructing propositions. The discussion includes defining arithmetic expressions and their evaluation through inductive propositions. The instructor illustrates how to create rules for evaluating expressions, such as constants, variables, and operations like addition and multiplication. The lecture also explores the concept of partial and non-deterministic functions, demonstrating how inductive propositions can represent these ideas. The Collatz conjecture is introduced as an example of a non-terminating sequence, showcasing the flexibility of inductive definitions. The instructor emphasizes the significance of choosing the right inductive proposition for proofs, highlighting the differences in reasoning when using inductive types versus inductive propositions. The session concludes with practical exercises, encouraging students to apply the concepts learned in defining and reasoning about inductive relations in Coq.