theorem Th37:
  A1 is open & A2 is open implies (A1 misses A2 iff A1,A2 are_separated)
proof
  assume
A1: A1 is open & A2 is open;
  thus A1 misses A2 implies A1,A2 are_separated
  proof
    assume A1 misses A2;
    then A1 misses Cl A2 & Cl A1 misses A2 by A1,Th36;
    hence thesis by CONNSP_1:def 1;
  end;
  thus thesis by CONNSP_1:1;
end;
