On Wed, 27 May 2020, Leonardo Romero wrote:
 $sudo apt-get build-dep gretl
 Reading package lists... Done
 E: You must put some 'source' URIs in your sources.list 
Yes. You need to modify your /etc/apt/sources.list files appropriately. 
You can do this by hand, or
1) Open synaptic (with root privileges)
2) Go to Settings > Repositories
3) Enable source code repositories
4) Reload the package information
Then everything should work
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   Riccardo (Jack) Lucchetti
   Dipartimento di Scienze Economiche e Sociali (DiSES)
   Università Politecnica delle Marche
   (formerly known as Università di Ancona)
   r.lucchetti(a)univpm.it
   
http://www2.econ.univpm.it/servizi/hpp/lucchetti
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