R help - Feb 2009 - lm function

Hi,

I do not use R lenguage for programming, hence Im trying to understand how
are specified the models below. I been reading some webpages with
information about the notation in the "lm" function, but havent
understand
exactly what does the ":" do. Can some one give me an explenation of
the
models below so I can replicate the results in other program.
 
#common intercept
mod2<-lm(TS~log(BodyWt)+log(BodyWt):factor(D),data=sleep2)
#paralell lines
mod3<-lm(TS~factor(D)+log(BodyWt)-1,data=sleep2)
#general
mod4<-lm(TS~factor(D)+log(BodyWt):factor(D)-1,data=sleep2)

TS is the dependent variable, log(bodyWt) is a covariate and D is either 1
or 2, depending in the case.

Thanks
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