Hello everyone.

Earlier, I used 'Stata' to build non-linear regressions.
Recently, I started using 'SEM' to solve new problems. I understood a bit the features that I need in 'SEM'. But I do not understand how to do what I did earlier in 'SEM'.

For example
To build a non-linear regression, I enter:
nl( Y = {c}+{x1}*x1+{x2}*x2+{x3}*x3+{x4}*x4)

In SEM :
sem (Y <- x1 x2 x3 x4)

In another case:
nl( Y = {c}+{x1}*ln(x1)+{x2}*sqrt(x2)+{x3}*x3+{x3}*x3*{x4} *x4)

But i don't know how to use 'sqrt', 'ln', and multiplication x3*x4 in SEM.

I read many different articles and topics, tried a lot of command options, but without success. Maybe I missed something or misunderstood, I apologize. But I hope for your help.
Thank you.