[dragonwriter]

> Do you accept that the following line is nominally linear?

> If you do, then you must accept that time is the only input to the supply function.

Er, no, even assuming the omitted x-axis is linear, I don't. The other inputs being relatively constant or having variation which mostly cancelled out each other's effects over a one year period is indistinguishable, on such a chart, from time being the only input. (Plus, the implicit function to which time would hypothetically be the only input isn't a supply function, which is a mapping from price to quantity people are willing to sell.)