diff --git a/src/app/cli/ArgDef.php b/src/app/cli/ArgDef.php
index 614414d..9664d36 100644
--- a/src/app/cli/ArgDef.php
+++ b/src/app/cli/ArgDef.php
@@ -35,6 +35,19 @@ class ArgDef {
     }
   }
 
+  protected ?string $extends = null;
+
+  function isExtends(): bool {
+    return $this->extends !== null;
+  }
+
+  protected ?bool $disabled = null;
+  protected ?array $removes = null;
+  protected ?array $adds = null;
+
+  protected ?array $args = null;
+  public ?string $argsdesc = null;
+
   protected ?bool $ensureArray = null;
   protected ?int $action = null;
   protected ?func $func = null;
@@ -44,10 +57,19 @@ class ArgDef {
   protected ?string $property = null;
   protected ?string $key = null;
 
+  public ?string $help = null;
+
   protected function parse(array $def): void {
     [$options, $params] = cl::split_assoc($def);
 
-    $this->extends = $params["extends"] ?? null;
+    $this->extends ??= $params["extends"] ?? null;
+
+    $this->disabled = vbool::withn($params["disabled"] ?? null);
+    $removes = varray::withn($params["remove"] ?? null);
+    A::merge($this->removes, $removes);
+    $adds = varray::withn($params["add"] ?? null);
+    A::merge($this->adds, $adds);
+    A::merge($this->adds, $options);
 
     $args = $params["args"] ?? null;
     $args ??= $params["arg"] ?? null;
@@ -59,13 +81,6 @@ class ArgDef {
 
     $this->argsdesc ??= $params["argsdesc"] ?? null;
 
-    $this->disabled = vbool::withn($params["disabled"] ?? null);
-    $adds = varray::withn($params["add"] ?? null);
-    A::merge($this->adds, $adds);
-    A::merge($this->adds, $options);
-    $removes = varray::withn($params["remove"] ?? null);
-    A::merge($this->removes, $removes);
-
     $this->ensureArray ??= $params["ensure_array"] ?? null;
     $action = $params["action"] ?? null;
     if ($action !== null) {
@@ -97,18 +112,6 @@ class ArgDef {
     $this->help ??= $params["help"] ?? null;
   }
 
-  public bool $isHelp = false;
-  public bool $isRemains = false;
-  public bool $haveShortOptions = false;
-  public bool $haveLongOptions = false;
-  public bool $isCommand = false;
-
-  public bool $haveArgs = false;
-  public ?int $minArgs = null;
-  public ?int $maxArgs = null;
-  public ?string $argsdesc = null;
-
-  protected ?bool $disabled = null;
   protected ?array $options = [];
 
   function getOptions(): array {
@@ -116,13 +119,12 @@ class ArgDef {
     else return array_keys($this->options);
   }
 
-  protected ?array $removes = null;
-  protected ?array $adds = null;
-
   /** traiter le paramètre parent */
   function processOptions(): void {
     $this->removeOptions($this->removes);
+    $this->removes = null;
     $this->addOptions($this->adds);
+    $this->adds = null;
   }
 
   function addOptions(?array $options): void {
@@ -207,6 +209,16 @@ class ArgDef {
     unset($this->options[$option]);
   }
 
+  public bool $haveShortOptions = false;
+  public bool $haveLongOptions = false;
+  public bool $isCommand = false;
+  public bool $isHelp = false;
+  public bool $isRemains = false;
+
+  public bool $haveArgs = false;
+  public ?int $minArgs = null;
+  public ?int $maxArgs = null;
+
   /** mettre à jour le type d'option */
   protected function updateType(): void {
     $haveShortOptions = false;
@@ -236,14 +248,8 @@ class ArgDef {
     $this->isRemains = $isRemains;
   }
 
-  public ?array $extends = null;
-
-  function isExtends(): bool {
-    return $this->extends !== null;
-  }
-
   function processExtends(ArgDefs $argDefs): void {
-    $option = $this->extends[0] ?? null;
+    $option = $this->extends;
     if ($option === null) {
       throw new ArgException("extends: missing destination arg");
     }
@@ -266,8 +272,6 @@ class ArgDef {
     $dest->processOptions();
   }
 
-  protected ?array $args = null;
-
   /**
    * traiter les informations concernant les arguments puis calculer les nombres
    * minimum et maximum d'arguments que prend l'option
@@ -424,4 +428,22 @@ class ArgDef {
     }
     $this->name = $name;
   }
+
+  function debugInfos(): array {
+    return [
+      ...$this->getOptions(),
+      "empty" => $this->isEmpty(),
+      "help" => $this->help,
+      "have_short_options" => $this->haveShortOptions,
+      "have_long_options" => $this->haveLongOptions,
+      "is_command" => $this->isCommand,
+      "is_help" => $this->isHelp,
+      "is_remains" => $this->isRemains,
+      "ĥave_args" => $this->haveArgs,
+      "min_args" => $this->minArgs,
+      "max_args" => $this->maxArgs,
+      "args" => $this->args,
+      "argsdesc" => $this->argsdesc,
+    ];
+  }
 }
diff --git a/src/app/cli/ArgDefs.php b/src/app/cli/ArgDefs.php
index 1a35879..7d4d648 100644
--- a/src/app/cli/ArgDefs.php
+++ b/src/app/cli/ArgDefs.php
@@ -12,16 +12,24 @@ abstract class ArgDefs {
 
   protected array $defs;
 
-  protected function mergeParse(array $defs, ?array &$argDefs): void {
+  protected function mergeParse(array $defs, ?array &$argDefs, bool $parse=true): void {
     $defaults = $defs["defaults"] ?? null;
-    if ($defaults !== null) $this->mergeParse($defaults, $argDefs);
+    if ($defaults !== null) {
+      $this->mergeParse($defaults, $argDefs, false);
+      $this->parse($defaults, $argDefs);
+    }
 
-    $this->parse($defs, $argDefs);
+    if ($parse) $this->parse($defs, $argDefs);
 
     $merges = $defs["merges"] ?? null;
     $merge = $defs["merge"] ?? null;
     if ($merge !== null) $merges[] = $merge;
-    if ($merges !== null) $this->mergeParse($merges, $argDefs);
+    if ($merges !== null) {
+      foreach ($merges as $merge) {
+        $this->mergeParse($merge, $argDefs, false);
+        $this->parse($merge, $argDefs);
+      }
+    }
   }
 
   protected function parseParams(?array $params): void {
diff --git a/src/app/cli/SimpleArgDefs.php b/src/app/cli/SimpleArgDefs.php
index 4bf3d50..df19842 100644
--- a/src/app/cli/SimpleArgDefs.php
+++ b/src/app/cli/SimpleArgDefs.php
@@ -57,41 +57,55 @@ class SimpleArgDefs extends ArgDefs {
 
   protected function addAll(?array $argDefs): void {
     parent::addAll($argDefs);
-    $index = [];
+    $this->index = [];
     if ($argDefs !== null) {
-      # calculer les fusions
+      # calculer les options pour les objets déjà fusionnés puis indexer une
+      # première fois
       foreach ($argDefs as $argDef) {
         /** @var ArgDef $argDef */
         if (!$argDef->isExtends()) {
           $argDef->processOptions();
         }
       }
+      $this->index = [];
+      foreach ($argDefs as $argDef) {
+        if ($argDef->isExtends()) continue;
+        $options = $argDef->getOptions();
+        foreach ($options as $option) {
+          /** @var ArgDef $prevArgDef */
+          $prevArgDef = $this->index[$option] ?? null;
+          if ($prevArgDef !== null) $prevArgDef->removeOption($option);
+          $this->index[$option] = $argDef;
+        }
+      }
+
+      # puis traiter les extensions d'objets, calculer les options pour ces
+      # objets et indexer pour la deuxième fois
       foreach ($argDefs as $argDef) {
         /** @var ArgDef $argDef */
         if ($argDef->isExtends()) {
           $argDef->processExtends($this);
         }
       }
-
-      # indexer les arguments
+      $this->index = [];
       foreach ($argDefs as $argDef) {
         if ($argDef->isExtends()) continue;
         $options = $argDef->getOptions();
         foreach ($options as $option) {
           /** @var ArgDef $prevArgDef */
-          $prevArgDef = $index[$option] ?? null;
+          $prevArgDef = $this->index[$option] ?? null;
           if ($prevArgDef !== null) $prevArgDef->removeOption($option);
-          $index[$option] = $argDef;
+          $this->index[$option] = $argDef;
         }
       }
 
+      # puis calculer nombre d'arguments et actions
       foreach ($argDefs as $argDef) {
         if ($argDef->isExtends()) continue;
         $argDef->processArgs();
         $argDef->processAction();
       }
     }
-    $this->index = $index;
   }
 
   function get(string $option): ?ArgDef {
diff --git a/tests/app/cli/ArgDefTest.php b/tests/app/cli/ArgDefTest.php
index aaea1a0..074b7d9 100644
--- a/tests/app/cli/ArgDefTest.php
+++ b/tests/app/cli/ArgDefTest.php
@@ -13,6 +13,7 @@ class ArgDefTest extends TestCase {
     $argDef->processOptions();
     $argDef->processArgs();
     $argDef->processAction();
+    var_export($argDef->debugInfos()); #XXX
     self::assertSame($options, $argDef->getOptions());
     self::assertSame($haveShortOptions, $argDef->haveShortOptions, "haveShortOptions");
     self::assertSame($haveLongOptions, $argDef->haveLongOptions, "haveLongOptions");
@@ -155,4 +156,28 @@ class ArgDefTest extends TestCase {
       true, true, false,
       false, 0, 0, "");
   }
+
+  function testExtends() {
+    $ARGS1 = [
+      ["-o:", "--longo",
+        "name" => "desto",
+        "help" => "help longo"
+      ],
+      ["-a:", "--longa",
+        "name" => "desta",
+        "help" => "help longa"
+      ],
+    ];
+    $ARGS2 = [
+      "merge" => $ARGS1,
+      ["extends" => "-a",
+        "remove" => ["--longa"],
+        "add" => ["--desta"],
+        "help" => "help desta"
+      ],
+    ];
+    $argDefs1 = new SimpleArgDefs($ARGS1);
+    $argDefs2 = new SimpleArgDefs($ARGS2);
+    self::assertTrue(true);
+  }
 }