Your task is to find the number couple with the greatest difference from a given array of number-couples. 
All number couples will be given as strings and all numbers in them will be positive integers.  
For instance: ['56-23','1-100']; in this case, you should identify '1-100' as the number couple with the greatest difference and return it.
In case there are more than one option, for instance ['1-3','5-7','2-3'], you should identify whichever is first, so in this case '1-3'. 
If there is no difference, like so ['11-11', '344-344'], return false.
def diff(arr):
    r = arr and max(arr, key = lambda x : abs(eval(x)))
    return bool(arr and eval(r)) and r
def diff(arr):
    r = arr and max(arr, key = lambda x : abs(eval(x)))
    return bool(arr and eval(r)) and r