mean.acf <- function(x, ...){
##
## 1.  dots
##
  dots <- list(...)
##
## 2.  nd
##
  nd <- length(dots)
##
## 3.  checks
##
  classDots <- sapply(dots, function(x)inherits(x, 'acf'))
  if(any(!classDots))stop('Not all arguments of class acf')
#
  ndimx <- (dim(x$acf)[-1] == 1)
  if(any(!ndimx)) stop('x must be a univariate acf;  is not')
#
  ndimDots <- sapply(dots, function(x)all(dim(x$acf)[-1] == 1))
  if(any(!ndimDots)) stop('all arguments must be univariate; not so')
##
## 4.  x.
##
  x. <- x
##
## 5.  Lags
##
  Lags <- min(length(x$acf), sapply(dots, function(x)length(x$acf)))
##
## 6.  mean of (x, dots)$acf[1:Lags]
##
  sumAcf <- x$acf[1:Lags]
  for(i in 1:nd)
    sumAcf <- sumAcf+dots[[i]]$acf[1:Lags]
#
  x.$acf <- (sumAcf / (nd+1))
##
## 7.  n.used
##
  sumN <- x$n.used
  for(i in 1:nd)
    sumN <- sumN+dots[[i]]$n.used
#
  x.$n.used <- (sumN-nd)
##
## 8.  lag
##
  x.$lag <- array(0:(Lags-1), dim=c(Lags, 1, 1))
##
## 9.  x.$series
##
  ser <- list(x$series)
  for(i in 1:nd)
    ser[[i+1]] <- dots[[i]]$series
#
  x.$series <- ser
##
## 10.  done
##
  x.
}
