Domain_sig.With_Assume
Corresponds to the creation of a new basic block, accessible only if the condition is met. None means bottom.
Because the transfer functions imperatively change the context, they cannot use assume, that returns a new context. Temporarily, we provide this instead (it should be applied only to fresh symbolic variables and not modify the set of valuations of the other symbolic variables. In particular, the condition must never make the context bottom).
The good long-term solution would be to make every transfer function return a new Context.t option, viewing the context as some state monad.