a and a
fail.
a and x
YES!
a and x
fail.
x and x
YES!
x and x
fail.
x and x
YES!
x and x
fail.
x and x
YES!
x and x
fail.
x and x
YES!
x and x
fail.
x and x
YES!
x and a
YES!
x and a
fail.
x and a
YES!
x and a
fail.
a and a
YES!
a and  
fail.
a and  
fail.
286