Updated the notation for lifting in ProofMode docs

ProofMode.md

@@ -57,7 +57,7 @@ Introduction of logical connectives
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 - `iPureIntro` : turn a pure goal into a Coq goal. This tactic works for goals
-  of the shape `■ φ`, `a ≡ b` on discrete COFEs, and `✓ a` on discrete CMRAs.
+  of the shape `⌜φ⌝`, `a ≡ b` on discrete COFEs, and `✓ a` on discrete CMRAs.
 
 - `iLeft` : left introduction of disjunction.
 - `iRight` : right introduction of disjunction.