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I define a digraph as a set $V$ (vertexes) and a relation $E$ (edges) on $V$.

Morphisms of digraph are functions which preserve $E$.

So we have a category.

What are co-products in this category? (I am especially interested what are the canonical injections.)

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4  
Coproducts are disjoint unions: you can check this by hand. –  Zhen Lin Sep 9 '13 at 16:53
4  
Zhen means that $\coprod_i (V_i,E_i) = (\coprod_i V_i,\coprod_i E_i)$. –  Martin Brandenburg Sep 9 '13 at 17:04
    
@ZhenLin Please consider converting your comment into an answer, so that this question gets removed from the unanswered tab. If you do so, it is helpful to post it to this chat room to make people aware of it (and attract some upvotes). For further reading upon the issue of too many unanswered questions, see here, here or here. –  Julian Kuelshammer Sep 14 '13 at 14:52
    
@MartinBrandenburg Please consider converting your comment into an answer, so that this question gets removed from the unanswered tab. If you do so, it is helpful to post it to this chat room to make people aware of it (and attract some upvotes). For further reading upon the issue of too many unanswered questions, see here, here or here. –  Julian Kuelshammer Jun 3 at 9:01
    
I don't really care (especially since porton hasn't answered). –  Martin Brandenburg Jun 3 at 9:03

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