The aim of this paper is to provide a self-contained proof of a general case of the coarea inequality, also known as the Eilenberg inequality. The result is known, but we are not aware of any place that a proof would be written with all details. The known proof is based on a difficult result of Davies. Our proof is elementary and does not use Davies' theorem. Instead we use an elegant argument that we learned from Nazarov through MathOverflow. We also obtain some generalizations of the coarea inequality.
@article{AFM_2021_46_2_a21,
author = {Behnam Esmayli and Piotr Haj{\l}asz},
title = {The coarea inequality},
journal = {Annales Fennici Mathematici},
pages = {965--991},
year = {2021},
volume = {46},
number = {2},
language = {en},
url = {http://geodesic.mathdoc.fr/item/AFM_2021_46_2_a21/}
}
TY - JOUR
AU - Behnam Esmayli
AU - Piotr Hajłasz
TI - The coarea inequality
JO - Annales Fennici Mathematici
PY - 2021
SP - 965
EP - 991
VL - 46
IS - 2
UR - http://geodesic.mathdoc.fr/item/AFM_2021_46_2_a21/
LA - en
ID - AFM_2021_46_2_a21
ER -
Behnam Esmayli; Piotr Hajłasz. The coarea inequality. Annales Fennici Mathematici, Tome 46 (2021) no. 2, pp. 965-991. http://geodesic.mathdoc.fr/item/AFM_2021_46_2_a21/