theorem ThB37:
  {a} * {b} = {a * b}
proof
A1: -{b} + {a} + {b} = {(-b)} + {a} + {b} by ThB3
    .= {(-b) + a} + {b} by Th18
    .= {a * b} by Th18;
  {a} * {b} c= -{b} + {a} + {b} & {a} * {b} <> {} by ThB32,ThB33;
  hence thesis by A1,ZFMISC_1:33;
end;
