[R] degrees of freedom in lm() treatment contrasts

[Martin Henry H. Stevens]

Does anyone have a good (and specific) reference for an explanation for 
the calculation of degrees of freedom in treatment contrasts? I checked 
the indexes of Venables and Ripley 2002, Crawley 2002, and Neter et al. 
(Applied Linear Statistical Models, 4th ed.), as well as the lm code. I 
would happily accept a "verbal" email explanation as well.
Many thanks,
Hank Stevens

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