Avoiding blank row when adding aligned equations with flalign inside enumerate

Question

I need to avoid the blank row in the figure below which is added when I use flalign inside enumerate. How can I overcome this problem?

   \begin{enumerate}[label=\arabic*\textsuperscript{a}.]
    \item $T_S < T_i < 2 T_S$;
    \item \begin{flalign*}
        C_S &= T_1 - T_S \\
        C_i &= T_{i+1} - T_i \quad \forall i \neq n &&
    \end{flalign*}
    \end{enumerate}

Answer 1

I gues, that you looking for something like this:

This is not possible to achieve by flalign* but aligned in in-line math mode is promising:

\documentclass[rmp,reprint]{article}
\usepackage{amsmath}
\usepackage{enumitem}
\begin{document}
\begin{enumerate}[label=\arabic*\textsuperscript{a}.]
    \item $T_S < T_i < 2 T_S$;
    \item $\begin{aligned}[t]
        C_S &= T_1 - T_S \
        C_i &= T_{i+1} - T_i \quad \forall i \neq n &&
    \end{aligned}$
    \end{enumerate}
\end{document}