$ sudo apt-get update
$ sudo apt-get install libfltk1.3-compat-headers 

libfltk1.3-compat-headers is installed in your system.

Make ensure the libfltk1.3-compat-headers package were installed using the commands given below,

$ sudo dpkg-query -l | grep libfltk1.3-compat-headers *

You will get with libfltk1.3-compat-headers package name, version, architecture and description in a table

libfltk1.3-compat-headers package basic information: