which scientist is known for the poincaré–birkhoff–witt theorem and the witt's theorem ?
select distinct var_uri where brack_open var_uri dbo_knownFor dbr_Poincaré–Birkhoff–Witt_theorem sep_dot var_uri rdf_type dbo_Scientist sep_dot var_uri dbo_knownFor dbr_Witt's_theorem sep_dot brack_close