theorem Th75:
  LeftComp SpStSeq D c= UBD (L~SpStSeq D)
proof
  set f=SpStSeq D;
  set A=L~SpStSeq D;
  LeftComp f is_a_component_of A` & not LeftComp f is bounded by Th74,
GOBOARD9:def 1;
  then
A1: LeftComp f is_outside_component_of A;
  LeftComp f c= union{B where B is Subset of TOP-REAL 2: B
  is_outside_component_of A}
  proof
    let x be object;
    assume
A2: x in LeftComp f;
    LeftComp f in {B where B is Subset of TOP-REAL 2: B
    is_outside_component_of A} by A1;
    hence thesis by A2,TARSKI:def 4;
  end;
  hence thesis;
end;
