Oh yes, the set {a,b} such that a<>1, b<>1 becomes {a,a/(a-1} and {b/(b-1), b} for a+b = a*b exists and is real; however, if the tangent of 90 degrees is perpendicular to the tangent of 0 degrees and they equal infinity and 0 respectively, such that y/x = infinity when x approaches zero as close as we like and y/x approaches 0 when y=0, then for two lines to be perpendicular, if their slopes be multiplied together and equal one, they are said to be perpendicular, then infinity * 0 = 1 defines the cartesian plane by defining the perpendicularity of the x and y axes, and division by 0 is allowed in the denominator after all.