Vim
vim is a powerful editor. It has a steep initial learning curve. Many people in Maths use one of emacs or vim. vi is the predecessor of vim. vim can be run in either graphical or text mode.
To start vim in graphical mode, open a terminal window and type
gvim filename &
or select Applications -> Accessories -> GVim from the GNOME menus.
To start plain text vim, type "vim filename" in a terminal window.
gvim has a help menu, and vim has a tutorial called vimtutor which can be run in graphical mode by typing vimtutor -g
or in text mode by typing vimtutor
.
You can use google to search for vim tutorials.
More information at http://www.vim.org.