+ bot z3' = (top z3) scaled -1;
+
+ nw = unitvector (z2 - z3');
+ ne_dist = (nw rotated -90) * 0.5 trill_thin;
+ nw_dist = (trill_ne rotated 90) * 0.5 trill_thin;
+
+ z5 = whatever * trill_ne + (z1 - nw_dist);
+ z5 = whatever * nw + (z3' - ne_dist);
+
+ pat := z5
+ -- (z1 - nw_dist){-trill_ne}
+ -- (z1 + nw_dist){trill_ne}
+ -- (z3 + nw_dist){trill_ne}
+ .. top z3{right}
+ .. (z3 + ne_dist){-nw};
+ pat := pat
+ -- pat scaled -1 shifted (-feta_eps, -feta_eps)
+ -- cycle;
+ pat := pat shifted (offset, 0);
+ fill pat;
+