/usr/include/osl/effect/ is in libosl-dev 0.6.0-3.
This file is owned by root:root, with mode 0o755.
..
/usr/include/osl/effect/boardBitEffect.h
/usr/include/osl/effect/boardBitMask.h
/usr/include/osl/effect/effectedNumTable.h
/usr/include/osl/effect/liberty8.h
/usr/include/osl/effect/liberty8Table.h
/usr/include/osl/effect/moveSignature.h
/usr/include/osl/effect/numBitmapEffect.h
/usr/include/osl/effect/numSimpleEffect.h
/usr/include/osl/effect/numSimpleEffect.tcc
/usr/include/osl/effect/readme.h
/usr/include/osl/effect/signatureEffect.h
/usr/include/osl/effect_action/alwaysMove.h
/usr/include/osl/effect_action/betterToPromote.h
/usr/include/osl/effect_action/pieceFilter.h
/usr/include/osl/effect_action/promote.h
/usr/include/osl/effect_action/readme.h
/usr/include/osl/effect_action/simpleBetterToPromote.h
/usr/include/osl/effect_action/simpleMove.h
/usr/include/osl/effect_action/storePiece.h
/usr/include/osl/effect_action/storePtypeOSquare.h
/usr/include/osl/effect_util/additionalEffect.h
/usr/include/osl/effect_util/additionalOrShadow.h
/usr/include/osl/effect_util/effectUtil.h
/usr/include/osl/effect_util/effectUtil.tcc
/usr/include/osl/effect_util/neighboring25Direct.h
/usr/include/osl/effect_util/neighboring8Direct.h
/usr/include/osl/effect_util/neighboring8Effect.h
/usr/include/osl/effect_util/pin.h
/usr/include/osl/effect_util/readme.h
/usr/include/osl/effect_util/sendOffSquare.h
/usr/include/osl/effect_util/shadowEffect.h
/usr/include/osl/effect_util/unblockableCheck.h
/usr/include/osl/effect_util/unblockableEffect.h
/usr/include/osl/effect_util/virtualPin.h