.PS
scale = 100
linethick = 0.2*72

define wscale {
for x=0 to B.wid*2/scale do {
  line thick 0.4 up 0.2*scale from (x/2,0.5)*scale
  sprintf("%g",x/2) at last line.start below
  } 
}

#efine lightgray {"0.8 0.8 0.8"}
#efine lightgray {"lightgray"}

a[1] = 0
a[2] = 1
a[3] = 3
[]
for i = 1 to 3 by 2 do {[
  arrowhead = a[i]
  B: box ht 2.75*scale wid 6.5*scale with .sw at (0,0) outlined "lightgray"
  box thick 0.4 wid B.wid ht B.ht at B
  arrow <-> from B.w to B.e width 1*scale ht 1*scale
  wscale
  spline <-> from 1/3<B.sw,B.se> up B.ht then to 1/3<B.se,B.sw> \
    then up B.ht wid 1*scale ht 1*scale
  arc cw <-> from B+(B.ht,B.ht)/2 to B+(-B.ht,B.ht)/2 with .c at B \
    width 1.0*scale ht 1.0*scale
  ] with .nw at last [].sw}

.PE
