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;
