diff --git a/CHANGELOG.md b/CHANGELOG.md
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+++ b/CHANGELOG.md
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+# Changelog for `agreeing`
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to the
+[Haskell Package Versioning Policy](https://pvp.haskell.org/).
+
+## 0.1.0.0 - 2023-03-15
+
+	Initial version
diff --git a/LICENSE b/LICENSE
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--- /dev/null
+++ b/LICENSE
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+Copyright James Cranch (c) 2023
+
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+
+    * Neither the name of Author name here nor the names of other
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/README.md b/README.md
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--- /dev/null
+++ b/README.md
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+# agreeing
+
+A simple data structure helping us ask questions of the following
+sort: "does all this data have the same /BLANK/ and if so what is it?"
diff --git a/Setup.hs b/Setup.hs
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--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/agreeing.cabal b/agreeing.cabal
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--- /dev/null
+++ b/agreeing.cabal
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+cabal-version: 1.12
+
+-- This file has been generated from package.yaml by hpack version 0.35.0.
+--
+-- see: https://github.com/sol/hpack
+
+name:           agreeing
+version:        0.1.0.0
+synopsis:       Idiomatic data structure for agreement
+description:    Please see the README on GitHub at <https://github.com/jcranch/agreeing#readme>
+category:       Data
+homepage:       https://github.com/jcranch/agreement#readme
+bug-reports:    https://github.com/jcranch/agreement/issues
+author:         James Cranch
+maintainer:     j.d.cranch@sheffield.ac.uk
+copyright:      2023 James Cranch
+license:        BSD3
+license-file:   LICENSE
+build-type:     Simple
+extra-source-files:
+    README.md
+    CHANGELOG.md
+
+source-repository head
+  type: git
+  location: https://github.com/jcranch/agreement
+
+library
+  exposed-modules:
+      Data.Agreement
+  other-modules:
+      Paths_agreeing
+  hs-source-dirs:
+      src
+  ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wmissing-export-lists -Wmissing-home-modules -Wpartial-fields -Wredundant-constraints
+  build-depends:
+      base >=4.7 && <5
+  default-language: Haskell2010
+
+test-suite agreeing-test
+  type: exitcode-stdio-1.0
+  main-is: Spec.hs
+  other-modules:
+      LengthSpec
+      Paths_agreeing
+  hs-source-dirs:
+      test
+  ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wmissing-export-lists -Wmissing-home-modules -Wpartial-fields -Wredundant-constraints -threaded -rtsopts -with-rtsopts=-N
+  build-depends:
+      agreeing
+    , base >=4.7 && <5
+    , hspec >=2.7 && <2.11
+  default-language: Haskell2010
diff --git a/src/Data/Agreement.hs b/src/Data/Agreement.hs
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--- /dev/null
+++ b/src/Data/Agreement.hs
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+-- | A simple data structure helping us ask questions of the following
+-- sort: "does all this data have the same <BLANK> and if so what is
+-- it?"
+--
+-- For example:
+-- > doTheseHaveTheSameLength :: [String] -> String
+-- > doTheseHaveTheSameLength l = case foldMap (Somebody . length) of
+-- >   Somebody n -> "They all have length " <> show n
+-- >   Nobody     -> "The lengths differ"
+-- >   Anybody    -> "You didn't give me any strings"
+module Data.Agreement (
+  Agreement(..),
+  getSomebody,
+  ) where
+
+import Data.Semigroup (Semigroup(..),
+                       stimesIdempotentMonoid)
+
+-- | We have the following constructors:
+-- * `Somebody` is a consistent choice of an element.
+-- * `Nobody` is an inconsistent choice.
+-- * `Anybody` is a failure to make any choice.
+data Agreement a = Anybody | Somebody a | Nobody
+
+-- | This picks out consistent choices as `Just`.
+getSomebody :: Agreement a -> Maybe a
+getSomebody (Somebody x) = Just x
+getSomebody _ = Nothing
+
+instance Functor Agreement where
+  fmap _ Anybody = Anybody
+  fmap f (Somebody x) = Somebody (f x)
+  fmap _ Nobody = Nobody
+
+instance (Eq a) => Semigroup (Agreement a) where
+  Anybody <> x = x
+  Nobody <> _ = Nobody
+  Somebody x <> Anybody = Somebody x
+  Somebody _ <> Nobody = Nobody
+  Somebody x <> Somebody y
+    | x == y = Somebody x
+    | otherwise = Nobody
+  stimes = stimesIdempotentMonoid
+
+instance (Eq a) => Monoid (Agreement a) where
+  mempty = Anybody
diff --git a/test/LengthSpec.hs b/test/LengthSpec.hs
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+module LengthSpec (spec) where
+
+import Data.Agreement
+import Test.Hspec
+
+
+doTheseHaveTheSameLength :: [String] -> String
+doTheseHaveTheSameLength l = case foldMap (Somebody . length) l of
+  Somebody n -> "All have length " <> show n
+  Nobody     -> "The lengths differ"
+  Anybody    -> "No strings provided"
+
+
+spec :: Spec
+spec = do
+  describe "Testing whether strings have same length" $ do
+    it "works on strings of same length" $
+      doTheseHaveTheSameLength ["cat", "dog", "rat", "cow"] `shouldBe` "All have length 3"
+    it "works on single string" $
+      doTheseHaveTheSameLength ["crocodile"] `shouldBe` "All have length 9"
+    it "works on empty list" $
+      doTheseHaveTheSameLength [] `shouldBe` "No strings provided"
+    it "works on disparate strings" $
+      doTheseHaveTheSameLength ["sheep", "sheep", "sheep", "Archangel Gabriel", "sheep"] `shouldBe` "The lengths differ"
+
diff --git a/test/Spec.hs b/test/Spec.hs
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+++ b/test/Spec.hs
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+{-# OPTIONS_GHC -F -pgmF hspec-discover #-}
+-- Autodiscover spec files