@inbook{400185,
     title = {21. Exner an Bolzano},
     booktitle = {Bernard Bolzano's Schriften},
     series = {GDML\_Books},
     publisher = {Kr\'alovsk\'a \v cesk\'a spole\v cnost nauk},
     address = {Praha},
     year = {1935},
     pages = {106-107},
     url = {http://dml.mathdoc.fr/item/400185}
}