OK, some of the characters we know come from the regularization of the cursive form, like the radical 言 became 讠, etc. But how do I find how some really weird characters came from, like 舊->旧, 靈->灵, 異->异 and so on?
EDIT: To make it more clear, the above character are only examples. I'd like to know where they came up with the rules of EVERY AND EACH of the simplifications. Where do I find those rules?