🚀 go-pugleaf

On p. 124 of Goldberg (1989), it says that the sigma truncation function
is:

f' = f - (<f> - c*sigma)

      ^^^

On p. 62 of Michalewicz (1992) it says that the sigma truncation
function is:

f' = f + (<f> - c*sigma)

      ^^^

Is it plus or minus?  Goldberg cites Forrest (1985) as the original
source, but I do not have a copy.  Curiously enough, Michalewicz (1992) 
says that he is following Goldberg (1989). 

References

Forrest (1985). Documentation for PRISONERS DILEMMA and NORMS programs
that use the genetic algorithm.  Unpublished manuscript.  University of
Michigan, Ann Arbor.

Goldberg (1989). Genetic algorithms in search, optimization, and machine
learning.  Addison-Wesley.

Michalewicz (1992). Genetic algorithms + data structures = evolution
programs. Springer-Verlag.