Added example explanation to quantum-conveyor-belts program and small clarification to prob.md

Author: TianLangHin

competition/quantum-conveyor-belts/prob.md

@@ -52,6 +52,7 @@ ddd: drift(ccc); x(); y(ccc)
 ```
 
 Before you press any key, you can take a conveyor belt for free to go to station `bbb`.
+(This is denoted by `drift(bbb)` being on the `aaa:` line.)
 Thus, the very first superposition you reach is the set `{aaa, bbb}`.
 
 If you are in station `aaa`, pressing the `x` key on the conveyor belt

competition/quantum-conveyor-belts/src/main.rs

@@ -419,6 +419,16 @@ fn main() {
                 seeded_nfa == rebuilt_nfa
             );
         }
+        "example" => {
+            let example_nfa = Nfa::build_from(&[
+                "aju: drift(bkv); a(bkv, clw); b(clw)".to_string(),
+                "bkv: drift(dmx); a(bkv); b(bkv)".to_string(),
+                "clw: drift(); a(eny); b(bkv)".to_string(),
+                "dmx: drift(); a(); b(eny)".to_string(),
+                "eny: drift(dmx); a(aju, dmx); b(bkv, clw)".to_string(),
+            ]);
+            let _ = example_nfa.unreachable_superpositions(0, true);
+        }
         _ => panic!(),
     }
 }