/usr/include/GNUstep/ is in libsteptalk-dev 0.10.0-6build4.
This file is owned by root:root, with mode 0o755.
..
/usr/include/GNUstep/Frameworks/
/usr/include/GNUstep/Frameworks/StepTalk.framework/
/usr/include/GNUstep/Frameworks/StepTalk.framework/Headers
/usr/include/GNUstep/Frameworks/StepTalk.framework/Versions/
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/usr/include/GNUstep/Frameworks/StepTalk.framework/Versions/0/NSObject+additions.h
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/usr/include/GNUstep/StepTalk