: edge-pvertices ( edge -- pvertices ) [ [ end-pvertex>> ] [ start-pvertex>> ] bi dup , ! push the start pvertex and initialize the while loop [ 2dup eq? not ] [ next-pvertex>> dup , ] while ! keep pushing the next pvertex until we've pushed the end pvertex 2drop ! clear the stack elements we used to do the loop ] V{ } make ;