@book{MSMF_1989_2_39__1_0,
     author = {Helffer, B. and Sj\"ostrand, J.},
     title = {Semi-classical analysis for {Harper's} equation. {III} : {Cantor} structure of the spectrum},
     series = {M\'emoires de la Soci\'et\'e Math\'ematique de France},
     publisher = {Soci\'et\'e math\'ematique de France},
     number = {39},
     year = {1989},
     doi = {10.24033/msmf.346},
     zbl = {0725.34099},
     language = {en},
     url = {http://www.numdam.org/item/MSMF_1989_2_39__1_0/}
}