: edge-pvertices ( edge -- pvertices ) [ [ end-pvertex>> ] [ start-pvertex>> ] bi dup , ! initialize the loop and push the start pvertex [ 2dup eq? not ] [ [ next-pvertex>> dup , ] dip ] while ! push each additional pvertex up to and including the end pvertex 2drop ! clear the stack ] V{ } make ;