[R] A programming puzzler

[fharrell@virginia.edu]

I am trying to replicate part of the function of the
S-Plus terms.inner function.  I don't need an entire
model terms object but R expressions or character
strings containing the innermost variable name given
a vector of character strings or expressions.  Here
are some example inputs that each should result in the
string or expression "x":

x; x^2; g(x); h(g(x)); h(g(x^3)); j(h(g(pmin(x,3))))
h(g(x)+g(y))

To anyone who meets the challenge, thanks!

-- 
Frank E Harrell Jr              Prof. of Biostatistics & Statistics
Div. of Biostatistics & Epidem. Dept. of Health Evaluation Sciences
U. Virginia School of Medicine  http://hesweb1.med.virginia.edu/biostat
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