Passes the tests
Reveals intention
No duplication
Fewest elements
({}–>nil) no code at all->code that employs nil
(nil->constant)
(constant->constant+) a simple constant to a more complex constant
(constant->scalar) replacing a constant with a variable or an argument
(statement->statements) adding more unconditional statements.
(unconditional->if) splitting the execution path
(scalar->array)
(array->container)
(statement->recursion)
(if->while)
(expression->function) replacing an expression with a function or algorithm
(variable->assignment) replacing the value of a variable.