# How to define a new left-aligned environment?

I am working on preparing a document in latex, and I need to define an new environment as follow:

When the code is:

\begin{IF}
the sum of $a$, $b$, and $c$ is 10,\\
the product of $a$, $b$, and $c$ is 14,\\
the sum of squares of $a$, $b$, and $c$ is 54;
\end{IF}


It is displayed like this:

IF: the sum of a, b and c is 10,
the product of a, b, and c is 14;
the sum of squares of a, b, and c is 54;


Note that:

1. the first sentence of the body is preceded by the keyword "IF", i.e., they are in the same line.
2. these three sentences in the body are left-aligned.

Can you help me define this IF-environment? Thankssssssss!!

Here's one option using a list with the help of enumitem:

\documentclass{article}
\usepackage{enumitem}
\usepackage{lipsum}

\newlength\mylen
\AtBeginDocument{\settowidth\mylen{IF:~}}

\newlist{MIF}{description}{1}
\setlist[MIF,1]{leftmargin=*,labelsep=0pt,itemindent=-\mylen}
\newenvironment{IF}
{\begin{MIF}\item[\textnormal{IF:~}]}
{\end{MIF}}

\begin{document}

\lipsum[4]
\begin{IF}
the sum of $a$, $b$, and $c$ is 10,\\
the product of $a$, $b$, and $c$ is 14,\\
the sum of squares of $a$, $b$, and $c$ is 54;
\end{IF}
\lipsum[4]

\end{document}


The result:

• \AtBeginDocument{\setlength}{\mylen}{IF:~}} – egreg Aug 9 '15 at 8:51