[R] getting a ~ character in LaTeX

[Vigirdas Mackevicius]

===8<==============Original message text===============
I am writing course notes in LaTeX.  In the part where I am describing
model-fitting functions in R I want to use a ~ character inline.  If I
am displaying an example of R code in its own environment I use the
alltt environment, which protects the ~ character.  I have forgotten
how to protect the ~ when I am writing something like
  The operator `~' is used to define a model formula in \R.
  The left hand side is evaluated as the response.  The right hand
  side can consist of several \Emph{terms} with special meanings

I welcome suggestions.
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In plainTeX, 
I use $\widetilde{\ }$. 
I think this must also work in LaTeX.
Vigirdas Mackevicius
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Vigirdas MACKEVICIUS
Department of Mathematics and Informatics
Vilnius University
Naugarduko 24
2600 Vilnius
Lithuania
e-mail: vigirdas.mackevicius at maf.vu.lt
www:    http://www.mif.vu.lt/~vigirdas  
fax:    (+370 2) 251585
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