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

theorem Th101:
  X c= Y & Z c= V & X overlaps Z implies Y overlaps V
proof
  assume that
A1: X c= Y and
A2: Z c= V;
  assume X overlaps Z;
  then Y overlaps Z by A1,Th100;
  hence thesis by A2,Th99;
end;
