[R] seq unexpected behavior

[Vries, Han de]

seq(0.1, 0.9 - 0.8, by = 0.1) gives the following error message:

Error in seq.default(0.1, 0.9 - 0.8, by = 0.1) : 
        wrong sign in 'by' argument

but seq(0.1, 0.8 - 0.7, by = 0.1) gives
[1] 0.1
(no error message)

Why do I get an error message in the first case?
Han



> sessionInfo()
R version 2.2.1, 2005-12-20, i386-pc-mingw32

attached base packages:
[1] "methods"   "stats"     "graphics"  "grDevices" "utils"
"datasets" 
[7] "base"   

(NB I also tried version 2.3.1 and got the same result - both versions
are precompiled)
  
> Sys.getlocale()
[1] "LC_COLLATE=English_United States.1252;LC_CTYPE=English_United
States.1252;LC_MONETARY=English_United
States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252"


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