Add proof observable to frontend parse service

Author: jgonggrijp

frontend/src/app/services/parse.service.ts

@@ -38,6 +38,16 @@ export class ParseService {
         this.parseResults$,
         this.clearOnNewProblem$
     );
+
+    public proofs$ = this.parse$.pipe(map(extractProofs));
+}
+
+function extractProofs(response: ParseResponse) {
+    const {entailment, contradiction} = response.data.proofs;
+    return {
+        entailment: nltk2tableau(entailment),
+        contradiction: nltk2tableau(contradiction),
+    };
 }
 
 const emptyTableau = (): any => ({nodes: []});