问题

>> :version

Version: 0.597

>> :mode polyn
Switch into polynomial mode.

>> symbol(a,b,c,d)
out> a is a variable for polynomial.
out> b is a variable for polynomial.
out> c is a variable for polynomial.
out> d is a variable for polynomial.

------------------------

>> (a+b)(c+d)
in> (a+b)*(c+d)

out> ac+2ad+bc
------------------------

这里正确答案应该是 ac+ad+bc+bd