def filter(perm):
if perm['<STR_LIT>'] != perm['<STR_LIT>']:<EOL><INDENT>return False<EOL><DEDENT>return True<EOL>
This function can be used to selectively filter out specific permutation
    combinations. It is called for every possible permutation of the variables
    in the permutations dict. It should return True for valid a combination of 
    permutation values and False for an invalid one. 

    Parameters:
    ---------------------------------------------------------
    perm: dict of one possible combination of name:value 
                  pairs chosen from permutations.