Links in ProofMode.md.

ProofMode.md

@@ -3,10 +3,10 @@ Tactic overview
 
 Many of the tactics below apply to more goals than described in this document
 since the behavior of these tactics can be tuned via instances of the type
-classes in the file `proofmode/classes`. Most notable, many of the tactics can
-be applied when the to be introduced or to be eliminated connective appears
-under a later, a primitive view shift, or in the conclusion of a weakest
-precondition connective.
+classes in the file [proofmode/classes](proofmode/classes). Most notable, many
+of the tactics can be applied when the to be introduced or to be eliminated
+connective appears under a later, a primitive view shift, or in the conclusion
+of a weakest precondition connective.
 
 Applying hypotheses and lemmas
 ------------------------------