Functional Programming in Lean by David Thrane Christiansen Copyright Microsoft Corporation 2023 This is a free book on using Lean 4 as a programming language. All code samples are tested with Lean 4 release 4.1.0. Release history January, 2024 This is a minor bugfix release that fixes a regression in an example program. October, 2023 In this first maintenance release, a number of smaller issues w