@article{JOLT_2015_25_2_a3,
     author = {Noriyuki Abe},
     title = {First extension groups of {Verma} modules and {<italic>R</italic>-polynomials}},
     journal = {Journal of Lie Theory},
     pages = {377--393},
     year = {2015},
     volume = {25},
     number = {2},
     url = {http://geodesic.mathdoc.fr/item/JOLT_2015_25_2_a3/}
}