reserve a,b,p,x,x9,x1,x19,x2,y,y9,y1,y19,y2,z,z9,z1,z2 for object,
   X,X9,Y,Y9,Z,Z9 for set;
reserve A,D,D9 for non empty set;
reserve f,g,h for Function;
reserve A,B for set;
reserve x,y,i,j,k for object;

theorem Th85:
  for a,b being set, f being Function st a in dom f & f.a = b
  holds a .--> b c= f
proof
  let a,b be set, f be Function;
  assume a in dom f & f.a = b;
  then [a,b] in f by FUNCT_1:1;
  then {[a,b]} c= f by ZFMISC_1:31;
  hence thesis by ZFMISC_1:29;
end;
