.PS
.ps 20
## figure 25
B1:	box invis "invoke"
	arrow from B1.se to (B1.se.x+linewid, B1.se.y-lineht)
	line dashed to (B1.se.x+3*linewid, B1.se.y-3*lineht)
	arrow to (B1.se.x+4*linewid, B1.se.y-4*lineht)
B2:	box invis "invoke" with .nw at (B1.se.x+4*linewid, B1.se.y-4*lineht)
##
	line from (B1.ne.x+linewid, B1.n.y+lineht/2) \
	     to   (B1.ne.x+linewid, B2.s.y-lineht/2)
	line from (B2.sw.x-linewid, B1.n.y+lineht/2) \
	     to   (B2.sw.x-linewid, B2.s.y-lineht/2)
##
.PE