A performance optimization that delays the building of virtual DOM nodes. Calling (view model) will definitely build some virtual DOM, perhaps a lot of it. Calling (lazy view model) delays the call until later. During diffing, we can check to see if model is referentially equal to the previous value used, and if so, we just stop. No need to build up the tree structure and diff it, we know if the input to view is the same, the output must be the same!

Same as lazy but checks on two arguments.

Same as lazy but checks on three arguments.