theorem Th35:
  (SpStSeq S)/.1 = NW-corner S
proof
  1 in dom<*NW-corner S,NE-corner S,SE-corner S*> by FINSEQ_1:81;
  hence (SpStSeq S)/.1 = <*NW-corner S,NE-corner S,SE-corner S*>/.1 by
FINSEQ_4:68
    .= NW-corner S by FINSEQ_4:18;
end;
