= Solution
After asserting and releasing the active-low Start pulse, a valid sequence is \b[$X_0\uparrow$, then $X_1\uparrow$, then $X_2\uparrow$], with each input held high through the relevant sampling interval. The first <JK flip-flop> has $J=X_0,K=0$ and is clocked by $X_1$, so the rising <clock edge> of $X_1$ samples $X_0=1$ and sets $Y_0=1$. Once that output has settled, a rising <clock edge> of $X_2$ clocks the second <JK flip-flop> with $J=Y_0=1,K=0$, setting $Y_1=1$.
The essential conditions concern sampled levels: $X_0$ must be high at a rising <clock edge> of $X_1$, and $Y_0$ must then be high at a rising <clock edge> of $X_2$. Separate edges with adequate <setup and hold time> avoid an ambiguous simultaneous transition.
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