@inproceedings{gunnar1969minimization,
title={Minimization problems for the functional sup_{$x$}$F$($x, f$($x$),$f′$($x$))},
author={Gunnar Aronsson},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203441497051103},
booktitle={Arkiv for Matematik},
volume={7},
number={6},
pages={509-512},
year={1969},
}
Gunnar Aronsson. Minimization problems for the functional sup_{$x$}$F$($x, f$($x$),$f′$($x$)). 1969. Vol. 7. In Arkiv for Matematik. pp.509-512. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203441497051103.