IR' is a powerful principle for in the context of dependent type-theory, for defining simultaneously a set U *inductively*, with a function T : U -> D *recursively*. D may belarge', eg the type of Sets, and a paradigm example is a universe of (codes for) sets. I will try to motivate and illustrate this principle. Using containers (a particular kind of endofunctor on Set), one can distill out the essence of IR in an extremely compact, memorable form. I will try to give a tour of the distillery.