Sampling point of Assertions

In reply to ben@SystemVerilog.us:

And my point is once the evaluation of the RHS of a <= w is done, no matter what you do to w, as long as the evaluation of RHS is not triggered again, the assignment to the RHS should not be affected. The evaluation means the RHS is 0,1,x or z, not the RHS is w. Definitely correct me if I’m wrong. Thanks.