Description: Swap the first two variables in an equation with addition on the right, converting it into a subtraction. Version of mvrraddd with a commuted consequent, and of mvlraddd with a commuted hypothesis. (Contributed by SN, 21-Aug-2024)
|- ( ph -> B e. CC )
|- ( ph -> C e. CC )
|- ( ph -> A = ( B + C ) )
|- ( ph -> B = ( A - C ) )
|- ( ph -> ( A - C ) = B )