Where is the syntax error

 Hello, 
 
As a exercise of Ocaml from the very beginning I have to write a function which display true if both are non zero .
 
So I tried this : 
 
let both_zero a b = a != 0 || b !=0   ;;
 
But I see then this very cryptic error message: 
 
bash: syntax error near unexpected token `;;
 
Roelof