# Expression Rules

Comparison operators

• == equal

• != not equal

• < less than

• > greater than

• <= less than or equal to

• >= greater than or equal to

Logical operators

• and

• or

Array operators

• contain

• not contain

General principles

An expression consists of conditions. For example, the expression (transaction_blockNumber == 1 or block_number == 2) consists of two conditions: (transaction_blockNumber == 1) and (block_number == 2) The expression can consist of one or more conditions. There have to be logical operators between the conditions.

The logical operator and means that both conditions within the expression must be true. For example, the expression (transaction_gas == 123 and block_number == 321) will be considered true, when the block number 321 will include the transaction with gas equal to 123.

The logical operator or , means that at least one of the conditions must be true. For example, the expression (transaction_gas == 123 or block_number == 321) will be considered true, when the block number 321 appears on the network, or when gas is equal to 123 in any transaction.

Principles of composing an expression

1. Substitute a prefix equivalent to the name of the Entity. For example, if you want to track the block number 42, the expression should be (block_number == 42) , for transaction and receipt (transaction_blockNumber == 42) and (receipt_blockNumber == 42) respectively.

2. Such variables as int or uint must be without quotes in the expression as specified in the examples above. Such variables as hex20 и hex32 must be in double quotes, for example, (transaction_transactionHash == "0x91e44d7d3d8ebb0b5a9e4b0a276c0124281750182dfac5abead8efc752e6246a")

3. Enclose the expression in round brackets.