Shortest way of creating combinations of array elements

[Schalk Cronjé]

I am trying to find the shortest method of creating pairs of values from 
two lists.

   def a = [ 1,2,3,4,5,6 ]
   def b = [ 'a','b','c' ]
   assert [ [ 1,'a'], [2,'a'], ... [5,'c'],[6,'c'] == f(a,b)

The question is what te shortest possible implementation f(a,b) looks like.

I know a.collect { item -> b.collect { [item,it] }  } should work, but 
wondering if there is something better.

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Schalk W. Cronjé
Twitter / Ello / Toeter : @ysb33r