How do I set value of a boolean variable using an expression?

There is System -> togggle boolean action, but it does not support values coming from other variables or expressions

There is System -> set value action, but inside a group it does not list the global boolean variables. Thus I can't use it to set a value.

How can I set a value of a boolean global variable from an expression?

e.g. variable: isMultiGlobal = isMultiLocal