diff --git a/api/crosswalks.py b/api/crosswalks.py
index 4ff56ad5..29394ea7 100644
--- a/api/crosswalks.py
+++ b/api/crosswalks.py
@@ -8,34 +8,16 @@ relator_contrib = {
 "arr" : "B25",
 "art" : "A07",
 "aui" : "A15",
-"aui" : "A16",
-"aui" : "A23",
-"aui" : "A24",
-"aui" : "A29",
 "aus" : "A03",
 "aut" : "A01",
-"aut" : "A38",
 "clb" : "A33",
 "cmm" : "A21",
-"cmm" : "E04",
 "cmp" : "A06",
 "cnd" : "D03",
 "com" : "C01",
-"com" : "C02",
-"com" : "C99",
 "cov" : "A36",
 "cre" : "A09",
-"cre" : "A10",
-"cre" : "A99",
 "ctb" : "A02",
-"ctb" : "A14",
-"ctb" : "A17",
-"ctb" : "A18",
-"ctb" : "A20",
-"ctb" : "A25",
-"ctb" : "A27",
-"ctb" : "A32",
-"ctb" : "A34",
 "ctg" : "A39",
 "cwt" : "A21",
 "dnc" : "E02",
@@ -43,22 +25,7 @@ relator_contrib = {
 "drt" : "D99",
 "dsr" : "A11",
 "edt" : "B01",
-"edt" : "B02",
-"edt" : "B04",
-"edt" : "B09",
-"edt" : "B12",
-"edt" : "B13",
-"edt" : "B14",
-"edt" : "B15",
-"edt" : "B16",
-"edt" : "B19",
-"edt" : "B20",
-"edt" : "B21",
-"edt" : "B23",
-"edt" : "B24",
 "ill" : "A12",
-"ill" : "A35",
-"ill" : "A40",
 "itr" : "E06",
 "ive" : "A44",
 "ivr" : "A43",
@@ -66,23 +33,102 @@ relator_contrib = {
 "lyr" : "A05",
 "lyr" : "A31",
 "nrt" : "B03",
-"nrt" : "B07",
-"nrt" : "E03",
-"nrt" : "E07",
 "pbd" : "B11",
 "pbl" : "B18",
 "pht" : "A08",
-"pht" : "A13",
-"pht" : "F01",
 "prf" : "E08",
-"prf" : "E99",
 "prg" : "A30",
 "pro" : "D01",
 "trl" : "B06",
-"trl" : "B08",
-"trl" : "B10",
 "voc" : "E05",
 }
+
+inv_relator_contrib = {
+"E01" : "act",
+"B05" : "adp",
+"B99" : "adp",
+"A19" : "aft",
+"A22" : "aft",
+"A37" : "ant",
+"B25" : "arr",
+"A07" : "art",
+"A15" : "aui",
+"A16" : "aui",
+"A23" : "aui",
+"A24" : "aui",
+"A29" : "aui",
+"A03" : "aus",
+"A01" : "aut",
+"A38" : "aut",
+"A33" : "clb",
+"A21" : "cmm",
+"E04" : "cmm",
+"A06" : "cmp",
+"D03" : "cnd",
+"C01" : "com",
+"C02" : "com",
+"C99" : "com",
+"A36" : "cov",
+"A09" : "cre",
+"A10" : "cre",
+"A99" : "cre",
+"A02" : "ctb",
+"A14" : "ctb",
+"A17" : "ctb",
+"A18" : "ctb",
+"A20" : "ctb",
+"A25" : "ctb",
+"A27" : "ctb",
+"A32" : "ctb",
+"A34" : "ctb",
+"A39" : "ctg",
+"A21" : "cwt",
+"E02" : "dnc",
+"D02" : "drt",
+"D99" : "drt",
+"A11" : "dsr",
+"B01" : "edt",
+"B02" : "edt",
+"B04" : "edt",
+"B09" : "edt",
+"B12" : "edt",
+"B13" : "edt",
+"B14" : "edt",
+"B15" : "edt",
+"B16" : "edt",
+"B19" : "edt",
+"B20" : "edt",
+"B21" : "edt",
+"B23" : "edt",
+"B24" : "edt",
+"A12" : "ill",
+"A35" : "ill",
+"A40" : "ill",
+"E06" : "itr",
+"A44" : "ive",
+"A43" : "ivr",
+"A04" : "lbt",
+"A05" : "lyr",
+"A31" : "lyr",
+"B03" : "nrt",
+"B07" : "nrt",
+"E03" : "nrt",
+"E07" : "nrt",
+"B11" : "pbd",
+"B18" : "pbl",
+"A08" : "pht",
+"A13" : "pht",
+"F01" : "pht",
+"E08" : "prf",
+"E99" : "prf",
+"A30" : "prg",
+"D01" : "pro",
+"B06" : "trl",
+"B08" : "trl",
+"B10" : "trl",
+"E05" : "voc",
+}
+
 iso639 = {
 "aa" : "aar",
 "ab" : "abk",