How to create a trigger checking strings differences

[videleaudubain]

Hi

I have two snmp items were type of information is text.
The returned values are checksums.

I want to create a trigger witch compare these two strings.
if value of item 1 is different than value of item 2, then alert. If value are the same then no alert.

I have tested this with no success:
{test-template:Node-1-Cluster-checksum.last(0)}#{test-template:Node-2-Cluster-checksum.last(0)}

the trigger is in unknow state : Format error or unsupported operator. Exp: [<item1 last value>]
regards