Set expressions allow you to define field values. A set expression must do the following:

• Be used in an aggregation function such as sum(), count(), min(), and so on
• Start with { and end with }

In the set expression {1-$<Product = {"Current Account"} >}, three distinctive parts can be defined: 

• Identifier: $
• Operator: the minus sign in 1-$
• Modifier: <Product = {"Current Account"} >