
theorem Th26:
  for C1, C2 being Coherence_Space for f being Function of C1,C2
for a being Element of C1 for y1,y2 being set st [a,y1] in graph f & [a,y2] in
  graph f holds {y1,y2} in C2
proof
  let C1, C2 be Coherence_Space;
  let f be Function of C1,C2;
  let a be Element of C1, y1,y2 be set;
  assume [a,y1] in graph f & [a,y2] in graph f;
  then y1 in f.a & y2 in f.a by Th24;
  then {y1,y2} c= f.a by ZFMISC_1:32;
  hence thesis by CLASSES1:def 1;
end;
