Function engine_held 

pub fn engine_held(
    build: &str,
    builds: &str,
    discriminators: &str,
    engine: &str,
) -> Result<(), ReceiptError>

Whether engine is the engine the build compiled and was made of discriminators: its SHA-256 the build row’s hw/rtl/logos_engine.v, and every module of it the oracle writes itself (Oracle::own_verilog) the text the oracle of discriminators writes now, byte for byte. A receipt is recorded under it; kept, the engine is held by its SHA-256 thereafter, so the oracle’s code may move on. The library the engine embeds (the engine’s crossing and ports, the store’s memory) is held by the build’s SHA-256 alone, so the library may move on between a build and its receipt; an own module that does not regenerate is refused by name.