anchor.diff:  [source,clojure-repl]
   ----
   $ clj
  -Clojure 1.9.0
  +Clojure 1.10.0
   user=> (in-ns 'myapp.never-created)
   #object[clojure.lang.Namespace 0x22356acd "myapp.never-created"]
   myapp.never-created=> (defn say-hello [x] (println "Hello, " x "!"))
  -CompilerException java.lang.RuntimeException: Unable to resolve symbol: defn in this context, compiling:(NO_SOURCE_PATH:2:1)
  +Syntax error compiling at (REPL:1:1).
  +Unable to resolve symbol: defn in this context
   ----
   
   **Explanation:** in this situation, https://clojure.github.io/clojure/clojure.core-api.html#clojure.core/in-ns[in-ns]
  
positive.code: [source,clojure-repl]
  ---- 
  $ clj ## APPROACH 3: manually copying the code of myproject.person-names in the REPL.
  Clojure 1.9.0
  (ns myproject.person-names
    (:require [clojure.string :as str]))
  
  
negative.code: [source,clojure-repl]
  ----
  $ clj
  Clojure 1.10.0
  user=> (ns myapp.foo-bar)
  nil
  myapp.foo-bar=> *ns*
  