diff --git a/metadata/entries/Epistemic_Logic.toml b/metadata/entries/Epistemic_Logic.toml
--- a/metadata/entries/Epistemic_Logic.toml
+++ b/metadata/entries/Epistemic_Logic.toml
@@ -1,34 +1,34 @@
 title = "Epistemic Logic: Completeness of Modal Logics"
 date = 2018-10-29
 topics = [
   "Logic/General logic/Logics of knowledge and belief",
 ]
 abstract = """
 This work is a formalization of epistemic logic with countably many
 agents. It includes proofs of soundness and completeness for the axiom
 system K. The completeness proof is based on the textbook
 \"Reasoning About Knowledge\" by Fagin, Halpern, Moses and
 Vardi (MIT Press 1995).
 The extensions of system K (T, KB, K4, S4, S5) and their completeness proofs
 are based on the textbook \"Modal Logic\" by Blackburn, de Rijke and Venema
 (Cambridge University Press 2001).
-Papers: <a href=\"https://doi.org/10.1007/978-3-030-88853-4_1\">https://doi.org/10.1007/978-3-030-88853-4_1</a>, <a href=\"https://doi.org/10.1007/978-3-030-90138-7_2\">https://doi.org/10.1007/978-3-030-90138-7_2</a>."""
+Papers: <a href=\"https://doi.org/10.1007/978-3-030-88853-4_1\">doi.org/10.1007/978-3-030-88853-4_1</a>, <a href=\"https://doi.org/10.1007/978-3-030-90138-7_2\">doi.org/10.1007/978-3-030-90138-7_2</a>."""
 license = "bsd"
 note = ""
 
 [authors]
 
 [authors.from]
 homepage = "from_homepage"
 
 [contributors]
 
 [notify]
 from = "from_email"
 
 [history]
 2021-04-15 = "Added completeness of modal logics T, KB, K4, S4 and S5."
 
 [extra]
 
 [related]
diff --git a/metadata/entries/FOL_Seq_Calc1.toml b/metadata/entries/FOL_Seq_Calc1.toml
--- a/metadata/entries/FOL_Seq_Calc1.toml
+++ b/metadata/entries/FOL_Seq_Calc1.toml
@@ -1,40 +1,40 @@
 title = "A Sequent Calculus for First-Order Logic"
 date = 2019-07-18
 topics = [
   "Logic/Proof theory",
 ]
 abstract = """
 This work formalizes soundness and completeness of a one-sided sequent
 calculus for first-order logic. The completeness is shown via a
 translation from a complete semantic tableau calculus, the proof of
 which is based on the First-Order Logic According to Fitting theory.
 The calculi and proof techniques are taken from Ben-Ari's
 Mathematical Logic for Computer Science.
-Paper: <a href=\"http://ceur-ws.org/Vol-3002/paper7.pdf\">http://ceur-ws.org/Vol-3002/paper7.pdf</a>."""
+Paper: <a href=\"http://ceur-ws.org/Vol-3002/paper7.pdf\">ceur-ws.org/Vol-3002/paper7.pdf</a>."""
 license = "bsd"
 note = ""
 
 [authors]
 
 [authors.from]
 homepage = "from_homepage"
 
 [contributors]
 
 [contributors.jensen]
 homepage = "jensen_homepage"
 
 [contributors.schlichtkrull]
 homepage = "schlichtkrull_homepage"
 
 [contributors.villadsen]
 homepage = "villadsen_homepage"
 
 [notify]
 from = "from_email"
 
 [history]
 
 [extra]
 
 [related]
diff --git a/metadata/entries/Public_Announcement_Logic.toml b/metadata/entries/Public_Announcement_Logic.toml
--- a/metadata/entries/Public_Announcement_Logic.toml
+++ b/metadata/entries/Public_Announcement_Logic.toml
@@ -1,29 +1,29 @@
 title = "Public Announcement Logic"
 date = 2021-06-17
 topics = [
   "Logic/General logic/Logics of knowledge and belief",
 ]
 abstract = """
 This work is a formalization of public announcement logic with
 countably many agents. It includes proofs of soundness and
 completeness for a variant of the axiom system PA + DIST! + NEC!. The
 completeness proof builds on the Epistemic Logic theory.
-Paper: <a href=\"https://doi.org/10.1007/978-3-030-90138-7_2\">https://doi.org/10.1007/978-3-030-90138-7_2</a>."""
+Paper: <a href=\"https://doi.org/10.1007/978-3-030-90138-7_2\">doi.org/10.1007/978-3-030-90138-7_2</a>."""
 license = "bsd"
 note = ""
 
 [authors]
 
 [authors.from]
 homepage = "from_homepage"
 
 [contributors]
 
 [notify]
 from = "from_email"
 
 [history]
 
 [extra]
 
 [related]