Hi Ed

Constrain.Equal is more commonly used for two random variables in which case it constrains the the two (previously defined) random variables to be equal.

Using it with a constant is equivalent to observing v, and there are many examples in the documentation where we observe random variables.

So, for example, if v is defined by a fixed distribution, there is nothing more to infer. Whereas if v is defined in terms of other random variables (for example it's defined in terms of a Gaussian with a random mean) then we can make inferences about those
other random variables by observing v.

John