My AC program gives wrong answer on test

4C
1
(C(C))2

formulas are equal, but my program doesn't agree with me.

<formula> ::= <sequence>             // <sequence>
<sequence> ::= <element><number>     // <element><number>
<number> ::= 2                       // <element>2
<element> ::= '(' <sequence> ')'     // (<sequence>)2
<sequence> ::= <element><element>    // (<element><element>)2
<element> ::= C                      // (C<element>)2
<element> ::= '(' <sequence> ')'     // (C(<sequence>))2
<sequence> ::= C                     // (C(C))2

Without some obvious steps.

Am I wrong?