improve documentation on core type system
improve documentation on core type system

Ignore-this: e0f33956d45b8a021c2fc52e4ff2b81f

darcs-hash:20090223131224-1a7c6-9445229f2cb9cd43600feebca08c387d1c39ae6c

kirbyfan64/jhc,kirbyfan64/jhc,kirbyfan64/jhc,kirbyfan64/jhc