Writing contracts is the fundamental purpose of Solidity. However, writing a contract demands sound error and exception handling. Errors and exceptions are the norm in programming and Solidity provides ample infrastructure for managing both. Writing robust contracts with proper error and exception management is one of the top best practices. Events are another important construct in Solidity. For all topics that we've discussed so far, we've seen a caller that invokes functions in contracts; however we have not discussed any mechanism through which a contract notifies its caller and others about changes in its state and otherwise. This is where events come in. Events are a part of event-driven programs where, based on changes within a program, it proactively notifies its caller about the changes. The caller is free to use this information...