reserve i,j,e,u for object;
reserve I for set; 
reserve x,X,Y,Z,V for ManySortedSet of I;

theorem Th94:
  X (\) Y = X (\+\) (X (/\) Y)
proof
A1: X (/\) Y c= X by Th15;
  thus X (\) Y = X (\) (X (/\) Y) by Th70
    .= (X (\) (X (/\) Y)) (\/) EmptyMS I by Th22,Th43
    .= X (\+\) (X (/\) Y) by A1,Th52;
end;
