Install gnustep-core-devel by entering the following commands in the terminal:
sudo apt update sudo apt install gnustep-core-devel
Description:
GNUstep Development Environment -- core libraries
These are the packages needed to develop programs for the GNUstep environment. . This is a metapackage that depends on the GNUstep core libraries (FoundationKit and AppKit, aka GNUstep Base and GUI).
Homepage: http://gnustep.org
Version: 7.9
Section: universe/x11