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@@ -14,11 +14,15 @@ So far, we are working the first step of the project : help to convey messages a
 This can be achieved by drawing from a bag marbles colour-coded with respect to their probability. How can this colour be understood as this year's flood return period ? 
 
 This stage is the opportunity to discuss these notions, and understand that colors represent a class of return periods : on a total of 100 marbles:
+- 90 black marbles : their occurrence is on average 9 times out of 10 : 9 floods in ten years are "SMALLER" THAN the 10-yr return period flood. 
+Therefore, the remaining 10 marbles represent floods  "BIGGER" THAN the 10-yr return period flood. Among these : 
 - $`\textcolor{green}{ \text{the 8 green marbles}}`$ mean floods with a return period between the 10-yr and the 50-yr return period,
 - $`\textcolor{blue}{ \text{the only blue marble}}`$  represents floods with a return period between the 50-yr and the 100-yr return period, 
 - $`\textcolor{red}{ \text{the red marble}}`$ represents thus $`\textcolor{red}{ \text{all the other, higher floods : floods with a return period OVER 100-yr.}}`$ It means that the reference "100-yr flood" does not occur as such once in 100 years, but it is EXCEEDED once in 100 years.
 
- Check that all these probabilities  ( 8 + 1 + 1 ) / 100 add up to 10/100, meaning the probability of the remaining 90 black marbles is indeed 9/10 : 9 floods in ten are UNDER the the 100-yr return period.
+The probability of occurrence of floods "higher than the 50-yr return period" is the same as drawing one blue OR one red marble : ( 1 + 1 ) / 100,  so one in 50.
+
+We can also begin to discuss how we can "order" floods (we can sort discharges, but not so easily flood events), and if a flood event really has a return period strictly speaking.
 
 After this, we can move on to series of N years, and for this an app is very useful to automatically generate series of "floods".