[antlr-interest] why are these productions different

[John Tijoe]

Hello,
I was playing with antlrworks and tried to understand the SimpleCalc demo.
And tried to write the expr and the multexpr in a more readable way (at
least to me). But my expr and multexpr seem to be different. Can someone
tell me why they are different I always get the error:
SimpleCalc.g:31:10: [fatal] rule multExpr has non-LL(*) decision due to
recursive rule invocations reachable from alts 1,2.  Resolve by
left-factoring or using syntactic predicates or using backtrack=true option.
What Am I missing??

except from it:

WORKING --> expr    : multExpr ((PLUS | MINUS ) multExpr)*;

NOT WORKING --> expr    : multExpr PLUS multExpr
    | multExpr MINUS multExpr
    | multExpr
    ;

NOT WORKING --> multExpr : atom ((MULT | DIV) atom )*;

NOT WORKING --> multExpr : atom MULT atom
    | atom DIV atom
    atom
    ;

Best regard John


PS:
Whole grammar
grammar SimpleCalc;

tokens {
PLUS = '+' ;
MINUS = '-' ;
MULT = '*' ;
DIV = '/' ;
RPAREN = ')' ;
LPAREN = '(' ;
ASSIGN = '=' ;
}
/*----------------
* PARSER RULES
*----------------*/
prog    : stat+ EOF;

stat    : expr NEWLINE
    | ID ASSIGN expr NEWLINE
    | NEWLINE; //Do nothing

expr    : multExpr ((PLUS | MINUS ) multExpr)*;

/*expr    : multExpr PLUS multExpr
    | multExpr MINUS multExpr
    | multExpr
    ;
*/

//multExpr : atom ((MULT | DIV) atom )*;

multExpr : atom MULT atom
    | atom DIV atom
    atom
    ;

atom : INT
    | ID
    | LPAREN expr RPAREN;
/*----------------
* LEXER RULES
*----------------*/
ID : ('a'..'z'|'A'..'Z')+;
INT : '0'..'9'+;
NEWLINE : '\r'?'\n';
WS : (' '|'\t'|'\n'|'\r')+;
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