[R] problems with plot()

[math_daddy]

I have a list of vectors of length 2, each representing a point in 2-space,
and each of which I wish to plot on the current plot. 
In a loop, I assign the x and y coordinates of the current element of the
list to variables 'x' and 'y' respectively, then make a call to plot as
follows:

par(new = TRUE)
plot(x,y, xlim = c(0,1),ylim=c(0,1), xlab <- "x", ylab <- "y",type =
"p",log="")

I must specify the input variable 'type', even though it defaults to "p",
because the previous call to plot() was used to plot lines, and so type is
set to "l". 
However, it is not clear to me why I must specify 'log'. It should still be
equal to "" since it was not changed in any previous call to plot(), but if
I do not specify it as above I get (4 of) the following message:

Warning messages:
1: In plot.window(...) :
  nonfinite axis limits [GScale(-inf,0,1, .); log=1

I would like to know the reason for this. Also, if my variables are named
anything other than 'x' and 'y', the x and y axes are not labeled according
to the xlab and ylab values I set in my call to plot. Why is this?

Thank you very much.
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