cmake find package failed

[zhaofeng]

System: Ubuntu 18.04
CMake Version: 3.10.2
Problem: with find_package(lemon REQUIRED), cmake cannot find lemon.

CMake Error at preflow/CMakeLists.txt:6 (find_package):
  By not providing "Findlemon.cmake" in CMAKE_MODULE_PATH this project has
  asked CMake to find a package configuration file provided by "lemon", but
  CMake did not find one.

  Could not find a package configuration file provided by "lemon" with any of
  the following names:

    lemonConfig.cmake
    lemon-config.cmake

  Add the installation prefix of "lemon" to CMAKE_PREFIX_PATH or set
  "lemon_DIR" to a directory containing one of the above files. If "lemon"
  provides a separate development package or SDK, be sure it has been
  installed.

However, /usr/lib/cmake/LEMONConfig.cmake is installed.
I believe the config file name and position are wrong.