Example 6.4.3.Consider the following system of equations for the three unknowns A, B, and C:
A = aAc + B
B = bB + C
C = _ + C.
These equations do not have a unique solution. For instance, it can be seen that these equations have the solution A = B = C = (a+b+c)*.
But they also have the solution A = {am bn cm| m,n0}, B = b*, C = {_}.
Notice that< {am bn cm| m,n0}, b*, {_}> < (a+b+c)*, (a+b+c)*, (a+b+c)*>.
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