Down arrow? Probability question

[Office_Shredder]

A question on my probability problem set reads: If the sequence of events A_n is non-decreasing (i.e. A_n is a superset of A_n+1 for all n), prove the following

$$P[A_n] \downarrow P[\bigcap_{i=0}^\infty A_i]$$

I just need to know what the heck the down arrow means

 

[slearch]

I think it means that the probabilities on the left are a non-increasing sequence converging to the number on the right (that's what you have to prove).