--- proofs/signatures/drat.plf.orig	2019-04-09 10:14:31.000000000 -0600
+++ proofs/signatures/drat.plf	2019-09-09 17:42:41.118932870 -0600
@@ -322,7 +322,7 @@
 
 
 ; Do unit propagation on `f`, constructing a UP model for it.
-(program build_up_model ((f cnf)) clause
+(program build_up_model ((f cnf)) UPConstructionResult
          (match (unit_search f)
                 (USRBottom UPCRBottom)
                 (USRNoUnit (UPCRModel cln))
@@ -335,7 +335,7 @@
 
 ; Given some starting assignment (`up_model`), continue UP to construct a larger
 ; model.
-(program extend_up_model ((f cnf) (up_model clause)) clause
+(program extend_up_model ((f cnf) (up_model clause)) UPConstructionResult
          (do (clause_into_global up_model)
            (let result (build_up_model f)
              (do (clause_undo_into_global up_model)