General start rule question for a context free grammar Suppose I have a context free grammar described:  


  $S \rightarrow 0SS1$
     $S \rightarrow 1$
     $S \rightarrow \epsilon$  


Because the first rule is considered the start rule does that mean that this grammar could never generate a string that starts with 1 or can you apply the second $S$ rule first to generate the string?
Yes you can apply the second rule you have written if you'd like. Since $S$ is your start symbol, you can apply any of its productions when you begin. It might be clearer if you wrote it as follows (where $|$ denotes or):


  $S \rightarrow 0SS1 \; |\; 1 \; | \; \epsilon$