@article{TAC_2003_11_a13,
     author = {Anders Kock and Gonzalo E. Reyes},
     title = {Some calculus with extensive quantities:  
wave equation},
     journal = {Theory and applications of categories},
     pages = {321--336},
     publisher = {mathdoc},
     volume = {11},
     year = {2003},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/TAC_2003_11_a13/}
}