Force all comparisons in a "multicomp" object
  to have the same sign.  If the contrast "A-B" has a negative estimate,
  reverse it show the contrast "B-A" with a positive estimate.
  If a contrast name does not include a minus sign "-" and the
  contrast is reversed, then an informative message is printed.
multicomp.reverse(y, estimate.sign = 1, ...)"multicomp" object
If estimate.sign==1, reverse the negatives.
    If estimate.sign==-1, reverse the positives.
    Both the names of the comparisons and the numerical values are reversed.
    If estimate.sign==0, return the argument.
other arguments not used.
The result is a "multicomp" object containing the same contrasts
as the argument but with the sign of the contrasts changed as needed.
Heiberger, Richard M. and Holland, Burt (2004b). Statistical Analysis and Data Display: An Intermediate Course with Examples in S-Plus, R, and SAS. Springer Texts in Statistics. Springer. ISBN 0-387-40270-5.
Heiberger, Richard M. and Holland, Burt (2006). "Mean--mean multiple comparison displays for families of linear contrasts." Journal of Computational and Graphical Statistics, 15:937--955.
# NOT RUN {
## see example in multicomp.order
# }
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