a+0+0=1a + 0 + 0 = 1a+0+0=1
0+r+0=10 + r + 0 = 1 0+r+0=1
a+0+t=1a + 0 + t = 1 a+0+t=1
a+r+t=1a + r + t = 1a+r+t=1
