diff --git a/artefact.inc.php b/artefact.inc.php
index 6571089..6e9b0fd 100644
--- a/artefact.inc.php
+++ b/artefact.inc.php
@@ -87,17 +87,30 @@ class TaskmanArtefact
 
   function isSourcesAffected(int $idx) : bool
   {
-    return isset($this->sources_affected[$idx]) && $this->sources_affected[$idx];
+    if(!isset($this->sources_affected[$idx]))
+    {
+      $file_changes = $this->task->getFileChanges();
+      $sources = $file_changes != null ? $this->getChangedSources($idx) : $this->getSources($idx);
+      $this->sources_affected[$idx] = is_stale($this->getPath(), $sources);
+    }
+    
+    return $this->sources_affected[$idx];
   }
 
   function getAffectedSourcesIndices() : array
   {
-    return array_keys($this->sources_affected);
+    $indices = array();
+    foreach($this->sources_affected as $idx => $is_affected)
+    {
+      if($is_affected)
+        $indices[] = $idx;
+    }
+    return $indices;
   }
 
   function isStale() : bool
   {
-    return count($this->sources_affected) > 0;
+    return count($this->getAffectedSourcesIndices()) > 0;
   }
 
   function initSources()
@@ -106,7 +119,7 @@ class TaskmanArtefact
 
     $all_src_specs = $this->getSourcesSpec();
     //let's process a convenience special case
-    if(count($all_src_specs) > 0 && !is_array($all_src_specs[0]))
+    if(count($all_src_specs) > 0 && !is_array($all_src_specs[0]) && !is_int($all_src_specs[0]))
       $all_src_specs = [$all_src_specs];
 
     foreach($all_src_specs as $src_idx => $src_spec)
@@ -146,6 +159,18 @@ class TaskmanArtefact
           );
         }
       }
+      //references another artefact by its index
+      else if(is_int($src_spec))
+      {
+        $src_artefact = $this->task->getArtefact($src_spec);
+
+        foreach($src_artefact->getSourcesSpec() as $src_idx => $_)
+        {
+          $this->setSourcesFn($src_idx, fn() => $src_artefact->getSources($src_idx));
+        if($file_changes != null)
+          $this->setSourcesChangedFn($src_idx, fn() => $src_artefact->getChangedSources($src_idx));
+        }
+      }
       else
         throw new Exception("Unknown artefact '{$this->getPath()}' source type" . gettype($src_spec));
     }
@@ -153,17 +178,13 @@ class TaskmanArtefact
 
   function checkAffectedSources() : bool
   {
-    $file_changes = $this->task->getFileChanges();
-
+    //let's check if any source is affected
     foreach($this->getSourcesSpec() as $src_idx => $src_spec)
     {
-      $sources = $file_changes != null ? $this->getChangedSources($src_idx) : $this->getSources($src_idx);
-      if(is_stale($this->getPath(), $sources))
-      {
-        $this->sources_affected[$src_idx] = true;
+      if($this->isSourcesAffected($src_idx))
         return true;
-      }
     }
+
     return false;
   }
 }
diff --git a/taskman.inc.php b/taskman.inc.php
index 48d9a9d..f331723 100644
--- a/taskman.inc.php
+++ b/taskman.inc.php
@@ -168,10 +168,19 @@ class TaskmanTask
 
     try
     {
-      if($this->getArtefacts() && !$this->_checkIfArtefactsStale())
+      $level = count($TASKMAN_STACK); 
+
+      if($this->getArtefacts())
       {
-        $this->has_run[$args_str] = true;
-        return;
+        $bench = microtime(true);
+        $stale_found = $this->_checkIfArtefactsStale();
+        log(0, "***** ".str_repeat('-', $level)."task '" . $this->getName() . "' artefacts check done(" . 
+                       round(microtime(true)-$bench,2) . '/' .round(microtime(true)-$TASKMAN_START_TIME,2) . " sec.) *****\n");
+        if(!$stale_found)
+        {
+          $this->has_run[$args_str] = true;
+          return;
+        }
       }
 
       $this->is_running = true;
@@ -179,8 +188,6 @@ class TaskmanTask
 
       $TASKMAN_STACK[] = $this;
 
-      $level = count($TASKMAN_STACK)-1; 
-
       log(0, "***** ".str_repeat('-', $level)."task '" . $this->getName() . "' start *****\n");
 
       if(!$TASKMAN_NO_DEPS)