the smooth flow of the principa l ideas . Som e of these sections ar e quite elementar y
and contain only the results which are either well known or essentially known. The y
are intende d fo r th e reade r wh o is not familia r wit h suc h standar d facts . However ,
it seem s that som e results in less elementary sections , A4 and A 7 for example, hav e
never bee n state d i n the form s w e present them .