diff --git a/v4/cli.py b/v4/cli.py
index f9b93f2..a3bb780 100644
--- a/v4/cli.py
+++ b/v4/cli.py
@@ -12,41 +12,77 @@ def cli_greetUser(
   return c
 #}
 
-# Ask user to select another item to have a pair of selected items
+# Select item
+#
+# Conditions:
+# 1. Id is digit, in bounds and not hidden
 @llm_by_value
-def cli_shouldPromptSelection(
+def cli_selectItem(
   c: cli_Context
 ) -> cli_Context:
-  if (
-    c.recentField == "cMemory" and
-    c.cMemory.recentField == "selectedItems" and
-    len(c.cMemory.selectedItems) == 1
+  if not (
+    c.input.isdigit()
   ):
-    c.outputPromptSelection = "Select the second item now:"
-    c.recentField = "outputPromptSelection"
+    c.recentField = "none"
+    return c
+  #}
+
+    int(c.input) >= 1 and
+    int(c.input) <= c.cMemory.playfieldSize * 2 and
+    int(c.input) not in c.cMemory.hiddenItems
+  ):
+    # User ids start with 1 while memory module has ids starting with 0
+    # Convert cli item id to memory item id
+    c.cMemory.selectedId = int(c.input) - 1
+    c.cMemory = memory_selectItem(c.cMemory)
+    c.recentField = "cMemory"
     return c
   #}
   c.recentField = "none"
   return c
 #}
 
-# Select item
+# Ask user to select another item to have a pair of selected items
 @llm_by_value
-def cli_selectItem(
+def cli_shouldPromptSelection(
   c: cli_Context
 ) -> cli_Context:
   if (
-    c.input.isdigit()
+    c.recentField == "cMemory" and
+    c.cMemory.recentField == "selectedItems" and
+    len(c.cMemory.selectedItems) == 1
   ):
-    id = int(c.input)
-    c.cMemory = memory_selectItem(c.cMemory)
-    c.recentField = "cMemory"
+    c.outputPromptSelection = "Select the second item now:"
+    c.recentField = "outputPromptSelection"
     return c
   #}
   c.recentField = "none"
   return c
 #}
 
+# Report selection of invalid item ids
+#
+# Conditions:
+# 1. Index out of bounds: less than minimum
+# 2. Index out of bounds: greater than maximum
+# 3. Item is already hidden
+#@llm_by_value
+#def cli_shouldReportInvalidItemSelection(
+#  c: cli_Context
+#) -> cli_Context:
+#  if (
+#    c.recentField == "cMemory" and
+#    c.cMemory.recentField == "selectedItems" and
+#    len(c.cMemory.selectedItems) == 1
+#  ):
+#    c.outputPromptSelection = "Select the second item now:"
+#    c.recentField = "outputPromptSelection"
+#    return c
+#  #}
+#  c.recentField = "none"
+#  return c
+##}
+
 # Show help (aka commands)
 @llm_by_value
 def cli_showHelp(
diff --git a/v4/cli_test.py b/v4/cli_test.py
index 27c8b9a..10faa91 100644
--- a/v4/cli_test.py
+++ b/v4/cli_test.py
@@ -1,5 +1,7 @@
 from cli import *
 from cli_Context import *
+from memory import *
+from memory_Context import *
 
 def cli_test_greetUser(
 ) -> str:
@@ -13,6 +15,51 @@ def cli_test_greetUser(
   return "ERR: cli_greetUser"
 #}
 
+def cli_test_selectItem(
+) -> str:
+  c = cli_createContext()
+  c.cMemory = memory_createContext()
+  c.input = "1"
+  c = cli_selectItem(c)
+  if (
+    c.recentField == "cMemory" and
+    c.cMemory.recentField == "selectedItems"
+  ):
+    return "OK: cli_selectItem"
+  #}
+  return "ERR: cli_selectItem"
+#}
+
+def cli_test_shouldPromptSelection(
+) -> str:
+  c = cli_createContext()
+  c.cMemory = memory_createContext()
+  c.input = "1"
+  c = cli_selectItem(c)
+  c = cli_shouldPromptSelection(c)
+  if (
+    c.recentField == "outputPromptSelection"
+  ):
+    return "OK: cli_shouldPromptSelection"
+  #}
+  return "ERR: cli_shouldPromptSelection"
+#}
+
+def cli_test_shouldReportIvalidItemSelection_outOfBoundsMin(
+) -> str:
+  c = cli_createContext()
+  c.cMemory = memory_createContext()
+  c.input = "0"
+  c = cli_selectItem(c)
+  c = cli_shouldReportInvalidItemSelection(c)
+  if (
+    c.recentField == "outputInvalidItemSelection"
+  ):
+    return "OK: cli_shouldReportInvalidItemSelection"
+  #}
+  return "ERR: cli_shouldReportInvalidItemSelection"
+#}
+
 def cli_test_showHelp_h(
 ) -> str:
   c = cli_createContext()
diff --git a/v4/main.py b/v4/main.py
index 125244e..d9bfc26 100644
--- a/v4/main.py
+++ b/v4/main.py
@@ -14,6 +14,9 @@ print(memory_test_shouldDetectVictory())
 print(memory_test_shouldHideMatchingItems())
 
 print(cli_test_greetUser())
+print(cli_test_selectItem())
+print(cli_test_shouldPromptSelection())
+print(cli_test_shouldReportIvalidItemSelection_outOfBoundsMin())
 print(cli_test_showHelp_h())
 print(cli_test_showHelp_help())
 
diff --git a/v4/memory.py b/v4/memory.py
index 1673e06..ad3fbd1 100644
--- a/v4/memory.py
+++ b/v4/memory.py
@@ -6,6 +6,8 @@ from llm import *
 ########
 
 # Generate constant playfield
+#
+# Both ids and group ids start with 0
 @llm_by_value
 def memory_generateConstPlayfield(
   c: memory_Context