We divide each sum to terms with \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$u \in \mathcal {L}^{\prime }$\end{document}u∈ℒ′ and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$u \notin \mathcal {L}^{\prime }$\end{document}u∉ℒ′: \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $$\begin{array}{*{20}l} &\sum\limits_{u \in \mathcal{L}^{\prime}} D^{\prime}_{uv}[a,b] + D^{\prime}_{uv}[c,d] + \\ &\underbrace{ D^{\prime}_{cv}[a,b] + D^{\prime}_{dv}[a,b] + D^{\prime}_{av}[c,d] + D^{\prime}_{bv}[c,d]}_{L} < \\ &\sum\limits_{u \in \mathcal{L}^{\prime}} D^{\prime}_{uv}[a,d] + D^{\prime}_{uv}[b,c] +\\ &\underbrace{D^{\prime}_{bv}[a,d] + D^{\prime}_{cv}[a,d] + D^{\prime}_{av}[b,c] + D^{\prime}_{dv}[b,c]}_{R1} =\\ &\sum\limits_{u \in \mathcal{L}^{\prime}} D^{\prime}_{uv}[a,c] + D^{\prime}_{uv}[b,d] +\\ &\underbrace{D^{\prime}_{bv}[a,c] + D^{\prime}_{dv}[a,c] + D^{\prime}_{av}[b,d] + D^{\prime}_{cv}[b,d]}_{R2} \end{array} $$ \end{document}∑u∈ℒ′Duv′[a,b]+Duv′[c,d]+Dcv′[a,b]+Ddv′[a,b]+Dav′[c,d]+Dbv′[c,d]⏟L<∑u∈ℒ′Duv′[a,d]+Duv′[b,c]+Dbv′[a,d]+Dcv′[a,d]+Dav′[b,c]+Ddv′[b,c]⏟R1=∑u∈ℒ′Duv′[a,c]+Duv′[b,d]+Dbv′[a,c]+Ddv′[a,c]+Dav′[b,d]+Dcv′[b,d]⏟R2