begin background
begin include
  X(a)
  X(b)
  X(b~Y)
  A1(x)
  A2(x)
  B(x)
  R1a(reverse)
  R1b(reverse)
  R3a(reverse)
  R3b(reverse)
end include
begin exclude
  A1(x!1).X(a!1)
  A2(x!1).X(a!1)
  B(x!1).X(b!1)
  X(b~pY)
end exclude
end background
