Chapter30 (v1) Object Equality: Equality in Scala
Chapter30 (v2) Object Equality: Writing an equality method
Chapter30 (v3) Writing equals: Changing equals without hashCode
Chapter30 (v4) Writing equals: Defining equals with the wrong signature
Chapter30 (v5) Writing equals: Changing equals without hashCode
Chapter30 (v6) Writing equals: Defining equals in terms of mutable fields