m <- lvm()
addvar(m) <- ~y1+y2+x
covariance(m) <- y1~y2
regression(m) <- c(y1,y2) ~ x
### Cancel the covariance between the residuals of y1 and y2
cancel(m) <- y1~y2
### Remove y2 from the model
rmvar(m) <- ~y2
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