diff --git a/00.brainstorming-pedagogical-teams/45.synthesis-structuring/instructions-for-levels/30.beyond/annex.fr.md b/00.brainstorming-pedagogical-teams/45.synthesis-structuring/instructions-for-levels/30.beyond/annex.fr.md
index 5f79c4b85..13315cbe0 100644
--- a/00.brainstorming-pedagogical-teams/45.synthesis-structuring/instructions-for-levels/30.beyond/annex.fr.md
+++ b/00.brainstorming-pedagogical-teams/45.synthesis-structuring/instructions-for-levels/30.beyond/annex.fr.md
@@ -181,12 +181,14 @@ Sont proposées les catégories suivantes, mais à débattre :
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! What is the optical system giving the image of the painting?
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+!
! * The optical system is composed of two spherical refracting surfaces, centered on the same optical axis.
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! How do you characterize each of the single optical elements that make up this optical system, and their relative distances?
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+!
! * The optical axis is oriented positively in the direction of light propagation (from the painting towards the lensball).
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! * The first spherical refracting surface $`DS1`$ encountered by the light has the follwing characteristics :