NOT.7:5.2 - Share a parameter while retaining a local exception

Three quoted amounts use the same tariff, 3 units per item, for quantities 2, 5 and 7. The expressions are 3*2, 3*5 and 3*7. Their intended common assumption is known, but the written expressions repeat it independently.

To make a common tariff change local, introduce p = 3 and write p*2, p*5 and p*7. A change to p = 4 then gives 8, 20 and 28. There is one tariff definition to change, while a reader of an individual expression now follows p to that definition. The definition must remain accessible.

The next request keeps the second quote at the old tariff and changes the others. A global change of p alone cannot express that request. Write the second expression as 3*5, with its fixed-tariff meaning stated, while the others remain p*2 and p*7. The amounts are now 8, 15 and 28. If later exceptions acquire their own shared rule, give that rule its own name.

For work dominated by common tariff changes, the shared parameter can be useful. For independently negotiated quotes, the assumption of a common tariff may be wrong. The notation repair therefore needs the subject’s sharing relation; identical printed numbers alone do not establish it.