diff --git a/pmwiki_recipes/exercises.php b/pmwiki_recipes/exercises.php
index 68c142f..a852e4e 100644
--- a/pmwiki_recipes/exercises.php
+++ b/pmwiki_recipes/exercises.php
@@ -15,12 +15,21 @@ error_reporting(0);
 #	what is the color hashing used in RevertedPIM for this group, color A, B or C?
 #		might require JS
 #	keyword or URL in pages
+#	definition of word and vice versa
+#		limited to pages with definitions (e.g. some languages)
+#			list lines with "* word = definition"
+#			split word and definition
+#			pick one and display the other with alternatives
 # implemented
 #	which of those page corresponds the updates visualization V, A, B or C? (type=historyvisualization)
 #	is page A linked to page B? (type=pagelink)
 # consider a difficulty parameter
 #	should be linked to the counter
 #	e.g. increasing the number of possibilities (at least 1 out of 5 pages instead of at least 1 out of 3)
+# XXX
+# 	picking a random page seems to fail from time to time
+#		some (very few) indices are not used, resulting in picked an empty string
+#		http://php.net/manual/en/function.array-rand.php seems to fix it
 
 
 $RecipeInfo['Exercises']['Version'] = '2011-12-08';
@@ -43,6 +52,17 @@ function Exercises($pagename, $auth){
 
 	$result = "";
 	$verbatimresult = "";
+
+	$n=3;
+	// n should be based on $difficulty, e.g. n=2+$difficulty or n=2^$difficulty
+	// it used to determine the number of false answers
+	// it can be overwritten per each exercise
+
+	$counterparam = "";
+	if ( $counter > 0) {
+		$counterparam = "counter=$counter&";
+	}
+
 	switch ($type){
 		case "pagelink":
 			// the pattern should be improve, e.g. remove PmWiki. , RecentChanges, GroupFooter, GroupHeader, Template, ...
@@ -58,8 +78,6 @@ function Exercises($pagename, $auth){
 			$sourcepage = $pages[rand(0,count($pages)-1)];
 
 			$content = ReadPage($sourcepage,READPAGE_CURRENT);
-			//$text = $content["text"];
-			// to use later on for expression exercises
 			$links = $content["targets"];
 			$links_array = explode(",",$links);
 
@@ -73,8 +91,6 @@ function Exercises($pagename, $auth){
 			unset($pages[array_search($answers[0],$pages)]);
 
 			//randomly pick n-1 others pages which may not be amongst the list of linked page
-			// n should be based on $difficulty, e.g. n=2+$difficulty or n=2^$difficulty
-			$n=3;
 			for ($i=1;$i<$n;$i++) {
 				$answers[] = $pages[rand(0,count($pages)-1)];
 				unset($pages[array_search($answers[$i],$pages)]);
@@ -83,11 +99,6 @@ function Exercises($pagename, $auth){
 			//display
 			$result .="Is page [[$sourcepage]] linked to ";
 
-			$counterparam = "";
-			if ( $counter > 0) {
-				$counterparam = "counter=$counter&";
-			}
-
 			// there should now be at least 1 needle in the haystack, the first one
 			// note that there might be more but this is not a problem as long as the question is stated clearly.
 			shuffle($answers);
@@ -134,8 +145,6 @@ function Exercises($pagename, $auth){
 			unset($pages[array_search($answers[0],$pages)]);
 
 			//randomly pick n-1 others pages which may not be amongst the list of linked page
-			// n should be based on $difficulty, e.g. n=2+$difficulty or n=2^$difficulty
-			$n=3;
 			for ($i=1;$i<$n;$i++) {
 				$answers[] = $pages[rand(0,count($pages)-1)];
 				unset($pages[array_search($answers[$i],$pages)]);
@@ -146,11 +155,6 @@ function Exercises($pagename, $auth){
 			$verbatimresult = $historyvisualization;
 			$result .="Which of those page corresponds the updates visualization:";
 
-			$counterparam = "";
-			if ( $counter > 0) {
-				$counterparam = "counter=$counter&";
-			}
-
 			// there should now be at least 1 needle in the haystack, the first one
 			// note that there might be more but this is not a problem as long as the question is stated clearly.
 			shuffle($answers);
@@ -163,10 +167,10 @@ function Exercises($pagename, $auth){
 					if ($group != "AllPages") {
 						list($currentgroup,$currentpage) = explode(".",$answers[$i]);
 						$result .="[[$pagename?action=ExercisesCheck&".$counterparam
-							."type=$type&source=$sourcepage&answer=".$answers[$i]."|".$currentpage."]], ";
+							."type=$type&source=$sourcepage&answer=".md5($answers[$i])."|".$currentpage."]], ";
 					} else {
 						$result .="[[$pagename?action=ExercisesCheck&".$counterparam
-							."type=$type&source=$sourcepage&answer=".$answers[$i]."|".$answers[$i]."]], ";
+							."type=$type&source=$sourcepage&answer=".md5($answers[$i])."|".$answers[$i]."]], ";
 					}
 				}
 			}
@@ -175,8 +179,82 @@ function Exercises($pagename, $auth){
 			// XXX checking of the result is not yet done, might have to hide (e.g. via hash) the answer and the source
 			break;
 		case "pagehasexpression":
-			// explode content by line "%0a" or word " "
-			$result .= "Does the page 'PAGE' has expression 'EXPRESSIONA', 'EXPRESSIONB' or 'EXPRESSIONC?";
+			// the pattern should be improve, e.g. remove PmWiki. , RecentChanges, GroupFooter, GroupHeader, Template, ...
+			if ($group == "AllPages"){
+				// equivalent to getting ALL pages
+				$pages = ListPages();
+			} else {
+				$pages = ListPages("/$group\./e");
+
+			}
+
+			//randomly pick a page in the possible pages
+			//$sourcepage = $pages[rand(0,count($pages)-1)];
+			$sourcepage = $pages[array_rand($pages)];
+			unset($pages[array_search($sourcepage,$pages)]);
+			$content = ReadPage($sourcepage,READPAGE_CURRENT);
+			$text = $content["text"];
+			$lines = explode("\n",$text);
+
+			// $links = $content["targets"];		
+			// $links_array = explode(",",$links);
+			// could be use for increase difficulty, e.g. pick content from related pages
+
+			//$answers = array();
+			//consider pilling up potential in $answers[]
+
+			$minlinelength = 20;
+			// this could also be consider a difficulty, the shorter the harder
+
+			//$answers[]["source"] = $sourcepage;
+			$pickedline = $lines[rand(0,count($lines)-1)];
+			unset($lines[array_search($pickedline,$lines)]);
+			while (( strlen($pickedline) < $minlinelength ) && ( count($lines) > 0 ) ) {
+				$pickedline = $lines[rand(0,count($lines)-1)];
+				unset($lines[array_search($pickedline,$lines)]);
+			}
+			//$answers[]["line"] = $pickedline;
+			$actualanswer = $pickedline;
+			$answers[] = $pickedline;
+
+			//randomly pick n-1 others pages which may not be amongst the list of linked page
+			for ($i=1;$i<$n;$i++) {
+				$otherpage = $pages[rand(0,count($pages)-1)];
+				$otherpage = $pages[array_rand($pages)];
+				unset($pages[array_search($otherpage,$pages)]);
+				$content = ReadPage($otherpage,READPAGE_CURRENT);
+				$text = $content["text"];
+				$lines = explode("\n",$text);
+				//$answers[]["source"] = $otherpage;
+				$pickedline = $lines[rand(0,count($lines)-1)];
+				unset($lines[array_search($pickedline,$lines)]);
+				while (( strlen($pickedline) < $minlinelength ) && ( count($lines) > 0 ) ) {
+					$pickedline = $lines[rand(0,count($lines)-1)];
+					unset($lines[array_search($pickedline,$lines)]);
+				}
+				//$answers[]["line"] = $pickedline;
+				$answers[] = $pickedline;
+			}
+
+			//display
+			$result .= "Does the page [[$sourcepage]] has expression ";
+
+
+			// there should now be at least 1 needle in the haystack, the first one
+			// note that there might be more but this is not a problem as long as the question is stated clearly.
+			shuffle($answers);
+
+			for ($i=0;$i<$n;$i++) {
+				if ($answers[$i]==$actualanswer)
+					$hashedanswer = md5($sourcepage);
+				else
+					$hashedanswer = md5($answers[$i]);
+				$result .="\n* [[$pagename?action=ExercisesCheck&".$counterparam
+					."type=$type&source=$sourcepage&answer=$hashedanswer|$i]] [@".$answers[$i]."@] ";
+				//should be better parsed!
+			}
+			$result .="\n\nClick on the answer.";
+			
 			break;
 		case "expressioninpage":
 			// explode content by line "%0a" or word " "
@@ -247,7 +325,7 @@ function ExercisesCheck($pagename, $auth){
 			}
 			break;
 		case "historyvisualization":
-			if ( $sourcepage == $answer ) {
+			if ( md5($sourcepage) === $answer ) {
 				$result .="Excellent! [[$sourcepage]] indeed has that history of editions.";
 				if ( $counter > 0) {
 					$counter++;
@@ -257,6 +335,23 @@ function ExercisesCheck($pagename, $auth){
 				}
 			} else {
 				$result .="No, it was the visualization of [[$sourcepage]] history of editions.";
+				// display it again
+				if ($counter > 0) $result .="\nIt means you are losing your $counter points.";
+				$result .="\n\nTry to redeem yourself by [[$pagename?action=Exercises&type=$type|trying another time]]. ";
+			}
+			break;
+		case "pagehasexpression":
+			if ( md5($sourcepage) === $answer ) {
+				$result .="Excellent! [[$sourcepage]] indeed has that expression.";
+				if ( $counter > 0) {
+					$counter++;
+					$result .="\n\nSee if you can [[$pagename?action=Exercises&type=$type&counter=$counter|solve yet another one]]. ";
+				} else {
+					$result .="\n\nSee if you can [[$pagename?action=Exercises&type=$type&counter=1|solve yet another one]]. ";
+				}
+			} else {
+				$result .="No, it was the expressoin of [[$sourcepage]].";
+				// display it again
 				if ($counter > 0) $result .="\nIt means you are losing your $counter points.";
 				$result .="\n\nTry to redeem yourself by [[$pagename?action=Exercises&type=$type|trying another time]]. ";
 			}