x1 is a right-angled shape/form defined by set of vertices x2, dimensions x3 (default 2).
Also rectangle, square, rectilinear; square (= kubykurfa, pitkubykurfa), cube (= kurkubli), rectangle (= clakurfa), rhombus/diamond (= sa'orkurfa, sa'orpitkubli). See also bliku, kubli, tapla, salpo, tarmi.