noConflict方法在库（accounting.js库）中如何工作？

Question

这是代码（具体来说是398到407）：

https://github.com/openexchangerates/accounting.js/blob/master/accounting.js#L403

我不明白这种方法：

// Use accounting.noConflict to restore `accounting` back to its original value.
// Returns a reference to the library's `accounting` object;
// e.g. `var numbers = accounting.noConflict();`
lib.noConflict = (function(oldAccounting) {
            return function() {
                // Reset the value of the root's `accounting` variable:
                root.accounting = oldAccounting;
                // Delete the noConflict method:
                lib.noConflict = undefined;
                // Return reference to the library to re-assign it:
                return lib;
            };
        })(root.accounting);

如果我执行var numbers = accounting.noConflict()，它将把库放在numbers变量中。我不明白的是，为什么我numbers.noConflict不确定。我知道lib.noConflict = undefined将其设置为undefined，但是由于下面的代码是lib，所以它不是然后设置为return lib吗？