diff --git a/core/vector/arithmetic.xml b/core/vector/arithmetic.xml
index bca17266..c687eb3b 100644
--- a/core/vector/arithmetic.xml
+++ b/core/vector/arithmetic.xml
@@ -26,50 +26,151 @@
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- Sum of vectors
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+ Sum of vectors
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+ \ref{_vproduct_} produces the product of two vectors:
+ $V_k = A_k B_k$.
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+ \ref{_vproduct} is its helper function for recursion.
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+ \ref{_mproduct_} produces the product of two matrices:
+ $M_{ij} = A_{ij} B_{ij}$.
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+ \ref{_mproduct} is its helper function for recursion.
+ \ref{_vproduct_} is used to reduce the problem to the product of
+ and array of~vectors.
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