The glpsol package is licensed under the GNU General Public License,
version 3 (GPL-3).

It includes one file from the GNU Linear Programming Kit (GLPK) 5.0,
unmodified:

  src/glpk/glpsol.c

    Copyright (C) 2000-2020 Free Software Foundation, Inc.
    License: GPL (>= 3)
    Source: https://ftp.gnu.org/gnu/glpk/glpk-5.0.tar.gz (examples/glpsol.c)

The original copyright and license header is retained in the file.

The GLPK library itself is not included; the package links against a
GLPK (>= 5.0) installation on the build system.