Algebraic Bowel Syndrome

What struck as a mental disorder exactly an year ago has now become a way of life. The 'algebraic bowel syndrome', which has a probability of affecting 1 in every 7 billion, is an obsessive compulsive disorder that strikes every morning, and only once, when the pants are down and the bottom is staring down the you-know-what. 

What are the symptoms of the disorder? There is only one, actually: the gate just won't open until a particular algebraic equation is solved. Sort of a daily math puzzle. The details:

1/ Consider each day as dd/mm/yy
2/ Now derive a f(dd,mm)=yy such that
        a/ Each of dd and mm should be used for equal number of times in the equation
        b/ The allowed operators are- +,-,*,/,!
3/ The aim is to solve this using dd and mm the least number of times

Example? Easy one this - 13/09/11
(13+13+9+9)/(13-9)=44/4=11

Aah. Relief.

With mm=yy, November '11 has been quite challenging and frustrating.