twisted relative to each other, leading to a very wide merged facet.
If so, error QH6271 is reported.  It may be overridden with option '<a href="qh-optq.htm#Q12">Q12</a>'.

<p>A "dupridge" may occur when the horizon facets for a new point is "pinched" (i.e., two vertices are
nearly adjacent).
If a subridge (e.g., a line segment in 3-d) is shared by two horizon facets, the four corresponding
new facets meet at the same ridge, called a "dupridge".
In poly_r.c, qh_matchnewfacets calls qh_matchneighbor.
qh_mat