4 premise to check for transaction validity
- First, if the consumed coins are valid, that is they really were created in previous transactions.
- Second, that the consumed coins were not already consumed in some previous transaction, this is not a double-spend.
- Third, that the total value of the coins that come out of this transaction is equal to the total value of the coins that went in.
- And finally that the transaction is validly signed by the owners of all of the consumed coins.