theorem
  mlt(<*c1*>,<*c2*>) = <*c1*c2*>
proof
  reconsider s1=c1, s2=c2 as Element of COMPLEX by XCMPLX_0:def 2;
  mlt(<*s1*>,<*s2*>) = <*multcomplex.(s1,s2)*> by FINSEQ_2:74
    .= <*c1*c2*> by BINOP_2:def 5;
  hence thesis;
end;
