\documentclass[12pt]{article}
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\begin{document}
\begin{equation*}
(\gamma_2\cdot \gamma_1)(t)=\theta(
\frac{1}{2} -t)\,\gamma_1(2\,t)+
\theta(t-\frac{1}{2})\,\gamma_2(2t-1)
\label{compo}
\end{equation*}
\end{document}