def lcat(L1,L2):
    """In : L1 (language : a set),
            L2 (language : a set).
       Out: L1 concat L2 (language : a set).
       Example:
       L1 = {'ab', 'bc'} 
       L2 = {'11', 'ab', '22'} 
       lcat(L1,L2) -> {'abab', 'bc22', 'ab11', 'ab22', 'bcab', 'bc11'}
    """
    return {x+y for x in L1 for y in L2}