SADT H-V-H Activity flow

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I am just beginning to learn Dia, with the interest of making some
SADT/IDEF-0 diagrams. I have loaded the shape sheet SADT, but I only
see on kind of activity flow: Vertical-Horizontal-Vertical. How do I
make the Horizontal-Vertical-Horizontal flow arrow that will be like
the VHV arrow? I read about deleting/adding segments, but then I can't
figure out how to make HVH shape work like the VHV shape (greying the
shape and arrow head) nor can I make sense of trying to get that new
HVH shape actually saved in the SADT sheet.