https://projecteuclid.org/download/pdf_1/euclid.acta/1485889650
https://projecteuclid.org/download/pdf_1/euclid.acta/1485891181
https://www.jstor.org/stable/pdf/1970740.pdf?refreqid=excelsior%3A709854bcd238764f22a8ffccb285331f
https://projecteuclid.org/download/pdf_1/euclid.jmsj/1240434774
https://projecteuclid.org/download/pdf_1/euclid.jmsj/1240434775
https://projecteuclid.org/download/pdf_1/euclid.jmsj/1240434494
https://projecteuclid.org/download/pdf_1/euclid.kjm/1250523693
https://projecteuclid.org/download/pdf_1/euclid.kjm/1250523653
https://projecteuclid.org/download/pdf_1/euclid.kjm/1250523654
https://gdz.sub.uni-goettingen.de/id/PPN235181684_0188?tify=%7B%22view%22%3A%22info%22%2C%22pages%22%3A%5B32%5D%7D
https://gdz.sub.uni-goettingen.de/id/PPN235181684_0225?tify=%7B%22view%22%3A%22info%22%2C%22pages%22%3A%5B281%5D%7D
https://projecteuclid.org/download/pdf_1/euclid.tmj/1178241332
https://projecteuclid.org/download/pdf_1/euclid.tmj/1178241333
https://projecteuclid.org/download/pdf_1/euclid.tmj/1178227652
https://www.jstor.org/stable/pdf/2118576.pdf?refreqid=excelsior%3A5cca84392523fcf6f176e2f8d2af5ee6
https://www.jstor.org/stable/pdf/2044999.pdf?refreqid=excelsior%3A6ff58a98dcd4f81180a676b2801340f0
https://www.jstor.org/stable/pdf/2160465.pdf?refreqid=excelsior%3Af890cabed95743769b4bdccf2583e5fe
https://projecteuclid.org/download/pdf_1/euclid.cmp/1103905359
https://gdz.sub.uni-goettingen.de/id/PPN356556735_0072?tify=%7B%22view%22%3A%22info%22%2C%22pages%22%3A%5B7%5D%7D
http://citeseerx.ist.psu.edu/viewdoc/download;jsessionid=B7BD734F2A5A8C10E55BAAC88F2DD1FC?doi=10.1.1.206.1532&rep=rep1&type=pdf
https://gdz.sub.uni-goettingen.de/id/PPN356556735_0053?tify=%7B%22view%22%3A%22info%22%2C%22pages%22%3A%5B171%5D%7D
https://projecteuclid.org/download/pdf_1/euclid.cmp/1104270948
https://www.jstor.org/stable/pdf/2318254.pdf?refreqid=excelsior%3A1d99a1e0e3881fc14adc92e2dbfa1876
https://projecteuclid.org/download/pdf_1/euclid.acta/1485888479
https://www.jstor.org/stable/pdf/1990945.pdf?refreqid=excelsior%3A62d84b16492446a4c6ce5c200df3255a
https://dl.acm.org/citation.cfm?doid=321992.321996
https://dl.acm.org/citation.cfm?id=321991
https://www.jstor.org/stable/pdf/1970637.pdf?refreqid=excelsior%3A922bc1c3ed82e732966fb6c9b05791b1
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC323452/pdf/pnas00314-0027.pdf