# Triangle

Determine if a triangle is equilateral, isosceles, or scalene.

An _equilateral_ triangle has all three sides the same length.<br/>
An _isosceles_ triangle has at least two sides the same length. (It is sometimes
specified as having exactly two sides the same length, but for the purposes of
this exercise we'll say at least two.)<br/>
A _scalene_ triangle has all sides of different lengths.

## Note

For a shape to be a triangle at all, all sides have to be of length > 0, and 
the sum of the lengths of any two sides must be greater than or equal to the 
length of the third side. See [Triangle Inequality](https://en.wikipedia.org/wiki/Triangle_inequality).

## Dig Deeper

The case where the sum of the lengths of two sides _equals_ that of the 
third is known as a _degenerate_ triangle - it has zero area and looks like 
a single line. Feel free to add your own code/tests to check for degenerate triangles.
## Setup

Check out [Exercism Help](http://exercism.io/languages/lisp) for instructions to
get started writing Common Lisp. That page will explain how to install and setup
a Lisp implementation and how to run the tests.

## Formatting

While Common Lisp doesn't care about indentation and layout of code,
nor whether you use spaces or tabs, this is an important consideration
for submissions to exercism.io. Excercism.io's code widget cannot
handle mixing of tab and space characters well so using only spaces is recommended to make
the code more readable to the human reviewers. Please review your
editors settings on how to accomplish this. Below are instructions for
popular editors for Common Lisp.

### VIM

Use the following commands to ensure VIM uses only spaces for
indentation:

```vimscript
:set tabstop=2
:set shiftwidth=2
:set expandtab
```

(or as a oneliner `:set tabstop=2 shiftwidth=2 expandtab`). This can
be added to your `~/.vimrc` file to use it all the time.

### Emacs

Emacs is very well suited for editing Common Lisp and has many
powerful add-on packages available. The only thing that one needs to
do with a stock emacs to make it work well with exercism.io is to
evaluate the following code:

`(setq indent-tab-mode nil)`

This can be placed in your `~/.emacs` (or `~/.emacs.d/init.el`) in
order to have it set whenever Emacs is launched.

One suggested add-on for Emacs and Common Lisp is
[SLIME](https://github.com/slime/slime) which offers tight integration
with the REPL; making iterative coding and testing very easy.

## Source

The Ruby Koans triangle project, parts 1 & 2 [http://rubykoans.com](http://rubykoans.com)

## Submitting Incomplete Solutions
It's possible to submit an incomplete solution so you can see how others have completed the exercise.