Function decide 

pub fn decide(
    left: &StreamSide<'_>,
    left_env: &Environment<'_>,
    right: &StreamSide<'_>,
    right_env: &Environment<'_>,
    functions: &[(String, String)],
    opts: &Options,
) -> Result<Report, StreamError>

Decide left against right, each under its environment, over their units, the functions of functions (each a left function, the right one proven equal to it) the only ones identified.