reserve x,y,z,a,b,c,X,A for set;
reserve C,D for Coherence_Space;
reserve T for Tolerance of union C;
reserve E for Tolerance of X;
reserve C,C1,C2 for Element of CSp(X);

theorem Th16:
  {x,y} in C implies x in union C & y in union C
proof
A1: {x} c= {x,y} & {y} c= {x,y} by ZFMISC_1:7;
A2: x in {x} & y in {y} by TARSKI:def 1;
  assume {x,y} in C;
  hence thesis by A1,A2,TARSKI:def 4;
end;
