Install etl-dev by entering the following commands in the terminal:
sudo apt update sudo apt install etl-dev
Description:
Extended Class and Template Library
ETL is a multi-platform class and template library designed to add new datatypes and functions which combine well with the existing types and functions from the C++ Standard Template Library (STL).
Homepage: http://www.synfig.org/
Version: 1.2.1-0.1
Section: universe/libdevel