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(ROOT_0 (S_0 (ATS_3 (ATS_1 (ATS_2 (SBAR_0 (WHNP_0 (WP_0 who)) (S_2 (VP_0 (TO_0 to) (VP_1 (VB_0 think) (S_2 (VP_0 (VBG_0 stepping))))))) (COMMA_0 ,)) (NP_0 (PRP_1 he))) (VP_3 (VBD_0 was))) (DOT_0 .)))