/usr/include/ompl/extensions/ is in libompl-dev 1.2.1+ds1-1build1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/ompl/extensions/morse/
/usr/include/ompl/extensions/morse/MorseControlSpace.h
/usr/include/ompl/extensions/morse/MorseEnvironment.h
/usr/include/ompl/extensions/morse/MorseGoal.h
/usr/include/ompl/extensions/morse/MorseProjection.h
/usr/include/ompl/extensions/morse/MorseSimpleSetup.h
/usr/include/ompl/extensions/morse/MorseStatePropagator.h
/usr/include/ompl/extensions/morse/MorseStateSpace.h
/usr/include/ompl/extensions/morse/MorseStateValidityChecker.h
/usr/include/ompl/extensions/morse/MorseTerminationCondition.h
/usr/include/ompl/extensions/opende/
/usr/include/ompl/extensions/opende/OpenDEControlSpace.h
/usr/include/ompl/extensions/opende/OpenDEEnvironment.h
/usr/include/ompl/extensions/opende/OpenDESimpleSetup.h
/usr/include/ompl/extensions/opende/OpenDEStatePropagator.h
/usr/include/ompl/extensions/opende/OpenDEStateSpace.h
/usr/include/ompl/extensions/opende/OpenDEStateValidityChecker.h
/usr/include/ompl/extensions/triangle/
/usr/include/ompl/extensions/triangle/PropositionalTriangularDecomposition.h
/usr/include/ompl/extensions/triangle/TriangularDecomposition.h