∵B is the proper subset of A, ∴B={ 1}, which means a- 1= 1, ∴a=2.
And c is a subset of a, then C=? , or C={ 1}, or C={2}, or C={ 1, 2}
When C=? ,δ = 4-4b
When C={ 1}, it means that b= 1 meets the requirements;
When C={2}, b=0, but at this time c = {0,2}, which is not satisfactory;
When C={ 1, 2}, it obviously does not meet the requirements.
To sum up, a=2, and b≥ 1.
Hope to adopt