align double map function

Question

i need write this map with this align.

i've tried this but is wrong

   \begin{align*}
\psi\colon A&\longrightarrow& B(D) \\
T&\longmapsto&\hat{T} \\
&&  \hat{T}\colon D     &\longrightarrow        \mathbb{C}   \\ 
S          &&&\longmapsto      \hat{T}(S)
\end{align*}

thanks

Answer 1

Use alignat to set another alignment point and then a nested aligned.

\documentclass{article}
\usepackage{amsmath,amssymb}

\begin{document}

\begin{alignat*}{2}
\psi\colon A&\rightarrow {}&& B(D) \\
           T&\mapsto     {}&& \hat{T} \\
&&&\begin{aligned}
  \hat{T}\colon D &\rightarrow \mathbb{C}   \\
                S &\mapsto     \hat{T}(S)
\end{aligned}
\end{alignat*}

\end{document}

Answer 2

A solution is an alignedat environment nested in align:

\documentclass{article}
\usepackage{mathtools, amssymb}

\begin{document}

\begin{align*}
\psi\colon A&\longrightarrow B(D) \\
T&\longmapsto \begin{alignedat}[t]{2} & \hat{T} \\
& \hat{T} & \colon D& \longrightarrow \mathbb{C} \\
 & & S& \longmapsto \hat{T}(S)
\end{alignedat}
\end{align*}

\end{document}