Function declare_unknowns 

pub fn declare_unknowns<Args: PartialEq + Clone + Debug + 'static>(
    ctx: &mut StepContext<'_>,
    args: &Args,
    generator: Make<Args, Vec<Unknown>>,
) -> GeopResult<()>

Declares the unknowns generator makes of args in the step being run, of the part’s Unknowns: of several declarations of one state, one that holds it fixed wins, and otherwise the first made. A plain function, like a make (Make).