Assertion to check a signal is stable between two pulses

In reply to Anjali:

HI Ben,
Thanks a lot for your quick replies.
In my case the signal A and B is a pulse of 1 clk cycle and sig rises 1clk after A rises and falls at the rising of signal B. There is random clks between pulse A and pulse B.
But by using the above assertion, I get assertion failure.

Thanks,
Anjali