(S (S (NP (BASENP (DT A) (JJ collaboratively-developed) (NN operating) (NN system) (NN kernel)) (VP (VBN known) (PP (IN as) (BASENP (NNP GNU) (NNP Hurd))))) (VP (VBZ has) (VP (VBN been) (VP (VP (VBN made) (S (ADJP (JJ bootable)))) (S (VP (VBG using) (NP (BASENP (DT the) (NN L4) (NN microkernel)) (COMMA ,) (SBAR (WHNP (WDT which)) (S (VP (VBZ provides) (NP (BASENP (NN room)) (PP (IN for) (NP (BASENP (JJ significant) (NN speed) (NNS improvements)) (PP (IN over) (NP (BASENP (DT an) (JJ existing) (NN implementation)) (VP (VBG using) (BASENP (DT the) (NN Mach) (NN microkernel)))))))))))))))))) (PERIOD .))