unable to parse correctly

Hi all

I am using antlr4 and i want to parse this:

```
(bits 64){
aaa
}
```

IF i delete this line **"code16_32 : 'aaa'"** in my grammar, it can parse, why? It shouldn't jump into rule "code16_32". Please help !!!

My grammar is :

```
grammar Assembler;

WS : [ \t]+ -> skip;
NL : '\r'? '\n' -> skip;
LINE_COMMENT : ';' ~[\r\n]*;
INSTRUCTION : [a-z]+;
IDENTIFIER : [a-zA-Z] [a-zA-Z0-9]+;
SECTION_NAME : '.' IDENTIFIER;
LABEL_POSTFIX : 'equ' ~[;]*;

assemble : lines
| EOF
;

lines : line*
;

line : bits64
;

comment : LINE_COMMENT
;

code16_32_64 : 'DUMMY'
;

code16 : 'DUMMY'
;

code16_32 : 'aaa' # aaa
| 'aad' # aad
| 'aad' IMM8 # aad_imm8
| 'aam' # aam
| 'aam' IMM8 # aam_imm8
| 'aas' # aas
| 'adc' AL ',' IMM8 # adc_imm8
| 'adc' AX ',' IMM16 # adc_imm16
;

code32 : INSTRUCTION
;

code32_64 : INSTRUCTION
;

code64 : INSTRUCTION {System.err.println("fuck");}
;

data : 'db' STRING ',' NUMBER
;

bits64 : '(bits 64){' (code64 | code32_64 | code16_32_64)* comment? '}'
;
```

Thanks
From Peter

Start with the sample input and the complete Assembler grammar in the issue, then trace how the lexer and parser select among code64, code32_64, code16_32_64, and code16_32. Run the grammar against the `(bits 64){ aaa }` example and compare behavior with and without the `code16_32` rule; done means explaining the differing parse result.

Written by the indexing model from the issue text.