how to construct a ex in GiNaC

[cbq]

I read the GiNaC code ,found a question.

Under GiNaC namespace ,the under code works well.

//***this is my code:
............
#include "ginac/ginac.h"
using namespace GiNaC;
............
int main(void)
{
      symbol a("a"),b("b");
      ex ex0(a+b);
      cout<<"ex0 = "<<ex0<<endl;
      return 0;
}
// end the code

but i find nothing about method ex(symbol) in GiNaC.
how  does the above statement
               ex  ex0(a)
work?


help me !!

thanks!

best regards,

Boqun Cheng

2003.10.17