Function substitute_one 

pub fn substitute_one<T>(
    substituted: &mut T,
    assigned: VariableID,
    linear: &Function,
) -> Result<(), SubstitutionError>
where
    T: Substitute<Output = T> + Clone,

In-place version of Substitute::substitute_one.

This clones the current value and commits the substituted value back only on success. If substitution fails, substituted is left unchanged. Use Substitute::substitute_one directly when you want explicit control over cloning or ownership.