/usr/include/Inventor/engines/ is in inventor-dev 2.1.5-10-16ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/Inventor/engines/SoBoolOperation.h
/usr/include/Inventor/engines/SoCalculator.h
/usr/include/Inventor/engines/SoCompose.h
/usr/include/Inventor/engines/SoComputeBoundingBox.h
/usr/include/Inventor/engines/SoConcatenate.h
/usr/include/Inventor/engines/SoCounter.h
/usr/include/Inventor/engines/SoElapsedTime.h
/usr/include/Inventor/engines/SoEngine.h
/usr/include/Inventor/engines/SoEngines.h
/usr/include/Inventor/engines/SoFieldConverter.h
/usr/include/Inventor/engines/SoGate.h
/usr/include/Inventor/engines/SoInterpolate.h
/usr/include/Inventor/engines/SoOnOff.h
/usr/include/Inventor/engines/SoOneShot.h
/usr/include/Inventor/engines/SoOutputData.h
/usr/include/Inventor/engines/SoSelectOne.h
/usr/include/Inventor/engines/SoSubEngine.h
/usr/include/Inventor/engines/SoTimeCounter.h
/usr/include/Inventor/engines/SoTransformVec3f.h
/usr/include/Inventor/engines/SoTriggerAny.h