anchor.diff:  myapp.ns1=> (ns myapp.ns2) ;; now switching to another namespace:
   nil
   myapp.ns2=> x ;; won't work, because x has not been defined in namespace `myapp.ns2`
  -CompilerException java.lang.RuntimeException: Unable to resolve symbol: x in this context, compiling:(NO_SOURCE_PATH:0:0)
  +Syntax error compiling at (REPL:0:0).
  +Unable to resolve symbol: x in this context
   myapp.ns2=> (str/upper-case "hello") ;; won't work, because alias `str` has not been defined in namespace `myapp.ns2`
  -CompilerException java.lang.RuntimeException: No such namespace: str, compiling:(NO_SOURCE_PATH:9:1)
  +Syntax error compiling at (REPL:1:1).
  +No such namespace: str
   ----
   
   == Switching to an existing namespace with `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 myproject.person-names)
  nil
  myproject.person-names=> nicknames ;; #'nicknames won't be defined, because the lib has not been loaded.
  Syntax error compiling at (REPL:0:0).
  Unable to resolve symbol: nicknames in this context
  myproject.person-names=> (require '[myproject.person-names]) ;; won't fix the situation, because the namespaces has already been created
  nil
  myproject.person-names=> nicknames
  Syntax error compiling at (REPL:0:0).
  Unable to resolve symbol: nicknames in this context
  ----
  