In reply to dave_59:
Hi Dave, I was studying this problem too, and thought that that Nonconsecutive operator would be a robust way to check that the signal in question was asserted 5 times;
Nonconsecutive Repetition
Nonconsecutive repetition specifies finitely many iterative matches of the operand Boolean expression, with a delay of one or more clock ticks from one match of the operand to the next successive match and no match of the operand strictly in between. The overall repetition sequence matches at or after the last iterative match of the operand, but before any later match of the operand.
sequence Write_4;
@(negedge clk) (!WR & RD) [=4]
endsequence
The Write_4 sequence describes 4 not necessarily consecutive writes to memory.