Dear All,
I cannot download a boost source from bintray, e.g.,
https://dl.bintray.com/boostorg/release/1.73.0/source/boost_1_73_0.tar.bz2
returns 403 Forbidden.
OTOH, sourceforge works:
https://sourceforge.net/projects/boost/files/boost/1.73.0/boost_1_73_0.tar.bz2.