.PS
.ps 20
## figure 12
B1:	box invis
	move to B1.e; \
	"\begin{tabular}[b]{r} STOR\\ open\\ send data\\ \ $\ldots$\\ close\end{tabular}\ " rjust
B2:	box invis height 6*boxht with .w at (B1.e.x+3*linewid, B1.e.y) \
	    "GATEWAY" width 3*boxwid/2
B4:	box invis with .s at B2.s "DISK" height 2*boxht
	arrow from (B2.c.x-boxwid/3, B2.c.y-boxht/2) to (B4.n.x-boxwid/3, B4.c.y+boxht/2)
	arrow from (B4.n.x+boxwid/3, B4.c.y+boxht/2) to (B2.c.x+boxwid/3, B2.c.y-boxht/2)
B3:	box invis height 6*boxht with .w at (B2.e.x+3*linewid, B2.e.y)
	move to B3.w; \
	"\ \begin{tabular}[t]{l} F-SELECT\\ F-OPEN\\ F-WRITE\\ F-DATA\\ \ $\ldots$\\ F-DATA-END\\ F-TRANSFER-END\\ F-CLOSE\\ F-DESELECT\end{tabular}" ljust
	arrow from (B1.e.x+linewid/2, B1.e.y) to (B2.w.x-linewid/2, B2.w.y)
	arrow from (B2.e.x+linewid/2, B2.e.y) to (B3.w.x-linewid/2, B3.w.y)
##
.PE