match step with
|PrecedingSibling,_,_ -> anc_st,par_st,Ata.StateSet.add a_dst pre_st,true
|(Parent|Ancestor|AncestorOrSelf),_,_ -> Ata.StateSet.add a_dst anc_st,par_st,pre_st,true
match step with
|PrecedingSibling,_,_ -> anc_st,par_st,Ata.StateSet.add a_dst pre_st,true
|(Parent|Ancestor|AncestorOrSelf),_,_ -> Ata.StateSet.add a_dst anc_st,par_st,pre_st,true