7.4 Rule statement quality 189 a requirement that each flight booking confirmation specify at least one passenger name. This require- ment can be expressed using numerous formulations, some invalid, others valid: for example, 1. {Each flight booking request must specify at least one passenger name (invalid: inappropriate term). 2. {Each flight booking confirmation must contain at least one passenger name (invalid: inappropriate verb phrase). 3. {There must be at least one passenger name in each flight booking confirmation (invalid: misplaced rule subject). 4. A flight booking confirmation must specify either one passenger name or more than one passenger name (valid: intended rule, unambiguous). 5. A flight booking confirmation must specify one or more passenger names (valid: intended rule, unambiguous). 6. A flight booking confirmation must specify at least one passenger name (valid: intended rule, unambiguous). 7. Each flight booking confirmation must specify at least one passenger name (valid: intended rule, unambiguous). Within the organization there may be a preference for one of the valid formulations over the others, or