def test_concatenation_aa(a):
    concAA = (a + a)
    assert (not concAA.accepts(''))
    assert (not concAA.accepts('a'))
    assert concAA.accepts('aa')
    assert (not concAA.accepts('aaa'))
    concAA = ((epsilon({'a', 'b'}) + a) + a)
    assert (not concAA.accepts(''))
    assert (not concAA.accepts('a'))
    assert concAA.accepts('aa')
    assert (not concAA.accepts('aaa'))
def test_concatenation_aa(a):
    concAA = (a + a)
    assert (not concAA.accepts())
    assert (not concAA.accepts('a'))
    assert concAA.accepts('aa')
    assert (not concAA.accepts('aaa'))
    concAA = ((epsilon({'a', 'b'}) + a) + a)
    assert (not concAA.accepts())
    assert (not concAA.accepts('a'))
    assert concAA.accepts('aa')
    assert (not concAA.accepts('aaa'))