A computer-implemented method, comprising: determining an unlocking transaction constraint that constrains an input of an unlocking transaction, the constraint being on the reference of the input of the unlocking transaction, or on parts of a previous transaction pointed to by said reference; creating a redeemable transaction, the redeemable transaction being the previous transaction, that includes: a transaction output that includes a redeemable amount; and a transaction locking script that includes the unlocking transaction constraint, wherein unlocking the redeemable amount is contingent upon execution by a verifier on a node of a blockchain network of: an unlocking script of the unlocking transaction, the unlocking script leaving serialized contents of the unlocking transaction on a stack, and then the transaction locking script, satisfying the unlocking transaction constraint; and wherein said execution of the transaction locking script by the verifier includes: verifying that the unlocking script contains certain data; extracting, from the input of the unlocking transaction included in the serialized contents of the unlocking transaction on the stack, the reference to the redeemable transaction's output; determining the constraint, which includes, if the constraint is on parts of the previous transaction, using the reference to cause injection of the previous transaction, after which the constraint can be applied to the fields of the previous transaction; and verifying the determined constraint; and causing the redeemable transaction to be validated at a node of a blockchain network. determining an unlocking transaction constraint that constrains an input of an unlocking transaction, the constraint being on the reference of the input of the unlocking transaction, or on parts of a previous transaction pointed to by said reference; creating a redeemable transaction, the redeemable transaction being the previous transaction, that includes: a transaction output that includes a redeemable amount; and a transaction locking script that includes the unlocking transaction constraint, wherein unlocking the redeemable amount is contingent upon execution by a verifier on a node of a blockchain network of: an unlocking script of the unlocking transaction, the unlocking script leaving serialized contents of the unlocking transaction on a stack, and then the transaction locking script, satisfying the unlocking transaction constraint; and a transaction output that includes a redeemable amount; and a transaction locking script that includes the unlocking transaction constraint, wherein unlocking the redeemable amount is contingent upon execution by a verifier on a node of a blockchain network of: an unlocking script of the unlocking transaction, the unlocking script leaving serialized contents of the unlocking transaction on a stack, and then the transaction locking script, satisfying the unlocking transaction constraint; and an unlocking script of the unlocking transaction, the unlocking script leaving serialized contents of the unlocking transaction on a stack, and then the transaction locking script, satisfying the unlocking transaction constraint; and wherein said execution of the transaction locking script by the verifier includes: verifying that the unlocking script contains certain data; extracting, from the input of the unlocking transaction included in the serialized contents of the unlocking transaction on the stack, the reference to the redeemable transaction's output; determining the constraint, which includes, if the constraint is on parts of the previous transaction, using the reference to cause injection of the previous transaction, after which the constraint can be applied to the fields of the previous transaction; and verifying the determined constraint; and verifying that the unlocking script contains certain data; extracting, from the input of the unlocking transaction included in the serialized contents of the unlocking transaction on the stack, the reference to the redeemable transaction's output; determining the constraint, which includes, if the constraint is on parts of the previous transaction, using the reference to cause injection of the previous transaction, after which the constraint can be applied to the fields of the previous transaction; and verifying the determined constraint; and causing the redeemable transaction to be validated at a node of a blockchain network.