source: Alteration or variation of the terms of this Agreement shall not be valid unless made in writing and signed and dated by the parties.
target: Alteration or variation of the terms of this Agreement shall not be valid. They shall be made in writing. They shall be signed and dated by the parties.
references: Alteration or variation of the terms of this Agreement shall not be valid. They shall be made in writing. They shall be signed and dated by the parties.