anyone knows automatic completation elisp script?

[litchi]

I wander anyone who knows an automatic completation tools~?
I mean if I want to input the word automatic
and I have inputed four characters a,u,t and o
then the rest (m,a,t,i,c) can be pushed to the screen automatilly
---need no complete command such as M-/

If only one word (eg, only the word automatic) matches the regular expression 
^auto 
no other words such as automatilly(this also match ^auto) exists in this buffer 
then we can use some keys to accept the auto completation(eg,<TAB>)
then if also some other matches,We can use some keys to change the one we 
wanted from
all the matches, eg, M-/.

Best regards
Litchi from China~~~

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