# NOT RUN {
x <- rfree(10,3)
y <- rfree(10,6)
z <- alpha(26)
sum(x)
abelianize(sum(x))
sum(x,y) == sum(sum(x),sum(y))
x+y # not the same!
sum(x,-x)
sum(x,rev(-x))
stopifnot(sum(x^z) == sum(x)^z)
# }
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