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<input type="Submit" name="button0" value="wert0">
<input type="Submit" name="button1" value="wert1">
<input type="Submit" name="button2" value="wert2">
<input type="Submit" name="button3" value="wert3">
<input type="Submit" name="button4" value="wert4">

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if(isset($button0)) berechne();
else if(isset($button1)) tueWasAnderes();
//...