/IncreaseCounter { /counter counter 1 add def } def
/trappath {
0 0 moveto 90 0 rlineto
-20 45 rlineto -50 0 rlineto
closepath
} def
/doATrap {
gsave
1 scalefactor scale
trappath
counter 2 mod
0 eq {.5} {0} ifelse
setgray fill
grestore
} def
250 350 translate
5 {IncreaseCounter doATrap DecreaseScale 0 20 translate} repeat
showpage