a、b 和 Y 之间应该存在哪个逻辑门/电路？

Question

Thanks for pondering over my question.
Above is a digital logic circuit with 2 inputs, & 1 output. I want following logic to be implemented in sequence:

1. b = 0, a = 0, Y = 0
2. b = 1, a = 0, Y = 1
3. b = 0, a = 1, Y = 1
4. b = 1, a = 1 should be explicitly avoided so that both a & b are not 1 simultaneously
5. Suppose step 3 is tried before step 2, then output should be 0, ie, Y = 0.

Which logic gate or digital circuit will work for above sequence of logical ops? I tried with OR and XOR gates, but they don't satisfy condition 5, and sequential operation can't be enforced.
Can I use 2-to-1 priority encoder such as the one shown in figure below?

Or may be some smart implementation of NOR SR latch? Please let me know of your thoughts. Thanks ahead of the time.

Answer 1

f XOR a seems to fit perfectly.

How is it that you feel it contradicts condition 1?

a b c F Y
---------
0 0 0 0 0
0 0 1 1 1
0 1 0 1 1
0 1 1 1 1
1 0 0 0 1
1 0 1 1 0
1 1 0 1 0
1 1 1 1 0