@article{MM2_1988__60_2_155266,
     author = {Olli Martio},
     title = {Counterexamples for unique continuation.},
     journal = {Manuscripta mathematica},
     pages = {21--48},
     publisher = {mathdoc},
     volume = {60},
     number = {2},
     year = {1988},
     zbl = {0653.30013},
     url = {http://geodesic.mathdoc.fr/item/MM2_1988__60_2_155266/}
}