global sign is positive ( we use different values in two calls of functions so that we finally check if all vector elements are 0.
if ( stk [ - 1 ] ) : NEW_LINE INDENT v [ ord ( s [ i ] ) - ord ( ' a ' ) ] += ( 1 if add else - 1 ) if adjSign ( s , i ) else ( - 1 if add else 1 ) NEW_LINE DEDENT