/usr/include/ is in libklatexformula3-dev 3.3.0~beta-1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/klfapp/
/usr/include/klfapp/klfmainwin.h
/usr/include/klfapp/klflibview.h
/usr/include/klfapp/klflibdbengine.h
/usr/include/klfapp/klflibentryeditor.h
/usr/include/klfapp/klfautoupdater.h
/usr/include/klfapp/klfmime.h
/usr/include/klfapp/klfuiloader.h
/usr/include/klfapp/klfpluginiface.h
/usr/include/klfapp/klfliblegacyengine.h
/usr/include/klfapp/klflibbrowser.h
/usr/include/klfapp/klfdbus.h
/usr/include/klfapp/klfmain.h
/usr/include/klfapp/klfstyle.h
/usr/include/klfapp/klfconfig.h
/usr/include/klfapp/klflatexsymbols.h
/usr/include/klfapp/klfsettings.h
/usr/include/klfapp/klfstylemanager.h
/usr/include/klfapp/klfcmdiface.h
/usr/include/klfapp/klflib.h
/usr/include/klfbackend/
/usr/include/klfbackend/klfblockprocess.h
/usr/include/klfbackend/klfbackend.h
/usr/include/klfbackend/klfuserscript.h
/usr/include/klfbackend/klffilterprocess.h
/usr/include/klfbackend/klflatexpreviewthread.h
/usr/include/klftools/
/usr/include/klftools/klfrelativefont.h
/usr/include/klftools/klfpobjeditwidget.h
/usr/include/klftools/klfflowlayout.h
/usr/include/klftools/klfutil.h
/usr/include/klftools/klffactory.h
/usr/include/klftools/klfenumlistwidget.h
/usr/include/klftools/klfpobj.h
/usr/include/klftools/klfsearchbar.h
/usr/include/klftools/klfdefs.h
/usr/include/klftools/klfprogerr.h
/usr/include/klftools/klfpathchooser.h
/usr/include/klftools/klfsidewidget.h
/usr/include/klftools/qtcolortriangle.h
/usr/include/klftools/klfdatautil.h
/usr/include/klftools/klfpixmapbutton.h
/usr/include/klftools/klfiteratorsearchable.h
/usr/include/klftools/klfunitinput.h
/usr/include/klftools/klfsysinfo.h
/usr/include/klftools/klflatexedit.h
/usr/include/klftools/klfconfigbase.h
/usr/include/klftools/klfflowlistwidget.h
/usr/include/klftools/klfadvancedconfigeditor.h
/usr/include/klftools/klfdisplaylabel.h
/usr/include/klftools/klfdebug.h
/usr/include/klftools/klfcolorchooser.h
/usr/include/klftools/klfguiutil.h
/usr/include/klftools/klfitemviewsearchtarget.h