reserve A,B,C,D,p,q,r for Element of LTLB_WFF,
        F,G,X for Subset of LTLB_WFF,
        M for LTLModel,
        i,j,n for Element of NAT,
        f,f1,f2,g for FinSequence of LTLB_WFF;

theorem th263pa:
  M |=0 F & M |=0 G iff M |=0 F\/G
proof
  hereby assume A1: M |=0 F & M |=0 G;
    thus M  |=0  F\/G
    proof
      let A;
      assume A in F\/G;
      then A in F or A in G by XBOOLE_0:def 3;
      hence M  |=0  A by A1;
    end;
  end;
  assume A2: M |=0 F\/G;
  thus M |=0 F
  proof
    let A;
    assume A in F;
    then A in F\/G by XBOOLE_0:def 3;
    hence M |=0 A by A2;
  end;
  let A;
  assume A in G;
  then A in F\/G by XBOOLE_0:def 3;
  hence M |=0 A by A2;
end;
