ab workouts

Can someone gimme some ab workouts that dont require machines or anything? because the gym i go to at school has no machines for abs! besides a sit up thing.
like things i can so with out equipment

 I would go with doin different types of crunches theres alot out there just have to find the right ones for u. Also u always need some cardio to get good abs and eat healthy. my suggestion tho is
-plain crunch
-reverse crunch
-double crunch
-bicycle crunch
-leg raises
-georgia Techs
 those r some of the best that i have found and i have tried them all just determine how many sets and rebs on ur own. Its different for everyone but just make sure u dont over work it and give them some time to rest. I know people say abs dont realli need much time to rest and they cant get over worked thats not true every muscle needs time to rest and  they can be overworked so work at ur own pace and youll get fast results if youll just do those xercises if u need more help just post. 

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-Bruce Lee

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do any of those crunches but with a weight.

 O yea i forgot to mention weighted crunch