This idea originates in homotopy theory and is due to Jardine, "Simplicial presheaves", JPAA 1987.
One can not take for $X$ any site, this definition only works in a topos with "enough points".
This idea originates in homotopy theory and is due to Jardine, "Simplicial presheaves", JPAA 1987.
One can not take for $X$ any site, this definition only works in a topos with "enough points".