dummy <- df(y, x, a, b, who)

who <- c("Joseph", "Kim", "Billy")

function() {
ols.reg.Billy <- lm(y ~ x + a + b, data = dummy[dummy$who == "Billy"])
dw.Billy <- dwtest(ols.reg.Billy)

output.Billy <- list(ols.reg.Billy, dw.Billy)
return(output.Billy)
}