/usr/lib/gcc/x86_64-linux-gnu/6/include/d/rt/util/ is in libgphobos-6-dev 6.4.0-17ubuntu1.
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..
/usr/lib/gcc/x86_64-linux-gnu/6/include/d/rt/util/array.d
/usr/lib/gcc/x86_64-linux-gnu/6/include/d/rt/util/container/
/usr/lib/gcc/x86_64-linux-gnu/6/include/d/rt/util/container/array.d
/usr/lib/gcc/x86_64-linux-gnu/6/include/d/rt/util/container/common.d
/usr/lib/gcc/x86_64-linux-gnu/6/include/d/rt/util/container/hashtab.d
/usr/lib/gcc/x86_64-linux-gnu/6/include/d/rt/util/container/treap.d
/usr/lib/gcc/x86_64-linux-gnu/6/include/d/rt/util/hash.d
/usr/lib/gcc/x86_64-linux-gnu/6/include/d/rt/util/random.d
/usr/lib/gcc/x86_64-linux-gnu/6/include/d/rt/util/string.d
/usr/lib/gcc/x86_64-linux-gnu/6/include/d/rt/util/typeinfo.d
/usr/lib/gcc/x86_64-linux-gnu/6/include/d/rt/util/utf.d