diff --git a/exercises/12_useful_modules/task_12_1.py b/exercises/12_useful_modules/task_12_1.py
index 46d7582..bcca74a 100644
--- a/exercises/12_useful_modules/task_12_1.py
+++ b/exercises/12_useful_modules/task_12_1.py
@@ -7,11 +7,14 @@
 The function expects a list of IP addresses as an argument.
 
 The function must return a tuple with two lists:
-* list of available IP addresses
-* list of unavailable IP addresses
-
-To check the availability of an IP address, use the ping command.
+* list of reachable IP addresses
+* list of unreachable IP addresses
 
+To check if an IP address is reachable, use the ping command (use subprocess).
+The IP address is considered reachable if the execution of the ping command
+completed with return code 0.
+Nuances: on Windows, the return code can be 0 not only when ping was successful,
+but it is the code that needs to be checked for the job. This is to simplify tests.
 
 Restriction: All tasks must be done using the topics covered in this and previous chapters.
 """
diff --git a/exercises/18_ssh_telnet/test_task_18_1a.py b/exercises/18_ssh_telnet/test_task_18_1a.py
index ddb6db8..e4a8f46 100644
--- a/exercises/18_ssh_telnet/test_task_18_1a.py
+++ b/exercises/18_ssh_telnet/test_task_18_1a.py
@@ -25,7 +25,7 @@ def test_function_return_value(capsys, first_router_wrong_pass):
     Function check
     """
     return_value = task_18_1a.send_show_command(first_router_wrong_pass, "sh ip int br")
-    correct_stdout = "Authentication fail"
+    correct_stdout = "authentication"
     out, err = capsys.readouterr()
     assert out != "", "Error message not printed to stdout"
-    assert correct_stdout in out, "Wrong error message printed"
+    assert correct_stdout in out.lower(), "Wrong error message printed"
diff --git a/exercises/20_jinja2/task_20_1.py b/exercises/20_jinja2/task_20_1.py
index 800e3d8..5fd2d04 100644
--- a/exercises/20_jinja2/task_20_1.py
+++ b/exercises/20_jinja2/task_20_1.py
@@ -13,6 +13,10 @@
 Check the operation of the function on the templates/for.txt template
 and data from the data_files/for.yml file.
 
+An important nuance: you need to get the directory from the template parameter,
+you cannot specify the current directory in the FileSystemLoader - that is,
+DO NOT do this: FileSystemLoader(".").
+Specifying the current directory will break the work of other tasks/tests.
 """
 import yaml
 
diff --git a/exercises/23_oop_special_methods/task_23_2.py b/exercises/23_oop_special_methods/task_23_2.py
index 679c546..3e9aec8 100644
--- a/exercises/23_oop_special_methods/task_23_2.py
+++ b/exercises/23_oop_special_methods/task_23_2.py
@@ -24,4 +24,6 @@
 *19:17:20.244 UTC Sat Apr 6 2019
 R1#
 
+The test checks the connection with parameters from the devices.yaml file.
+The file must contain the parameters of the available devices.
 """