Please help: combining elements of an array

Greetings, I've been banging my head against a wall trying to figure out how to do this... I've got an array that could contain any number of elements. I want to combine those elements in all possible ways (without repeating the same element in any given combination). For example: $list = array("A", "B", "C", "D"); $combo = combine($list); /* (This is the function I need help creating) */ After running this script, $combo would contain the following elements (though I don't really care if they're in this order or not): A B C D AB AC AD BA BC BD CA CB CD DA DB DC ABC ABD ACB ACD ADB ADC BAC BAD BCA BCD BDA BDC CAB CAD CBA CBD CDA CDB DAB DAC DBA DBC DCA DCB ABCD ABDC ACBD ACDB ADBC ADCB BACD BADC BCAD BCDA BDAC BDCA CABD CADB CBAD CBDA CDAB CDBA DABC DACB DBAC DBCA DCAB DCBA Notice that no elements contain the same letter more than once. This makes things a little more complicated, as in the real application the original elements may not be just letters, but words (and though preventing duplicate letters would be fairly simple, preventing duplicate words will be a bit harder, esp. if the list includes words such as 'the' and 'other'). For extra credit, allow me to specify a lower and upper limit on the number of terms that will be combined (i.e. if I specify limits of 2 and 3 the single letters and the four-letter combinations will be excluded.) Remember that the array could contain as few as one and as many as ?? elements. I'm sure I need some sort of recursive algorithm (i.e. the function calls itself), but I've never been too good at those, which is why I'm asking for help. Any ideas? (please reply directly to me as well as to the list, as I read the list through news.php.net and occasionally miss posts) TIA Scott Nicholson scottn@pnx1.com