Function instance_to_aif 

pub fn instance_to_aif(instance: &SchemeInstance) -> AifDocument

Export a crate::instance::SchemeInstance to an AIF document.

Mapping:

• each premise literal → one I-node
• the conclusion literal → one I-node
• the scheme instance → one RA-node whose scheme field names the scheme
• each critical question → one CA-node

Edges connect each premise I-node to the RA-node, the RA-node to the conclusion I-node, and each CA-node to the RA-node.

Node IDs are assigned as stringified sequential integers starting at 1 in a deterministic order (premises → conclusion → RA → CAs).