arrowsbest practices
What's the best practice to typeset Knuth's up-Arrow notation?
\uparrow and \upuparrow are relation symbols (according to unimath-symbols.pdf). But in Knuth's up arrow notation, these should be a binary operator. So, how should on treat this difference?
Secondly, should double up arrows be typeset as \upuparrow or as \uparrow\uparrow, which illustrates the double nature better.
Since \url switches to a "verbatim" mode it can't go in the argument of another command. You can go over this limitation, in this particular case, with the following code
\documentclass{article}
\usepackage{etoolbox,hyperref}
\newrobustcmd{\urlfootnote}[1]{%
\expandafter\footnote\expandafter{\expandafter\url\expandafter{\detokenize{#1}}}}
\begin{document}
The Activity Lifecycle is blah
blah\cite[Lifecycle\urlfootnote{http://developer.android.com/reference/android/app/Activity.html#Fragments}]{Google2012}.
\end{document}
Note that # doesn't need to be escaped.
If you replace some of the symbolism with words from natural language, I think you get a much clearer and cleaner result; the most natural choice for the list is an enumerate environment; here's one possibility:
\documentclass{article}
\usepackage{amsmath}
\usepackage{amssymb}
\begin{document}
We must have $(a^i,b^i,c^i) \in X^i(d)$, where $X^i(d)$ is the set of all triples $(a,b,c) \in \mathbb R^A \times \mathbb R^B \times \mathbb R^C $ such that
\begin{enumerate}
\item $d_0 \cdot (a_0 - b_0) + d_1 \cdot (b_0 - c_0) \leq 0$,
\item $\smash[b]{\sum_j c_j b^j} \leq d_j$, and
\item $\forall k \geq 1, d_k \cdot \left(a_k - b^h_k - F_k(x_{k^*})\right) \leq
\sum_k (b_k-c_k) \cdot \min\bigl(d_k \cdot G^j_k, m_k \bigr)$.
\end{enumerate}
\end{document}
Best Answer
There is a command
\mathbinfor creation of binary operators, so something likeworks.
As to your second questions, tastes differ