Hello,
in this book ( http://caml.inria.fr/pub/docs/fpcl/index.html ), there is 
the following grammar (chapter 10.3, on streams etc...) :

Expr ::= Mult
        | Mult + Expr
        | Mult - Expr

[...]

after factoring common prefixes, the author obtains :

Expr ::= Mult RestExpr

RestExpr ::= + Mult RestExpr
             |- Mult RestEXpr
             |(* nothing *)

[...]

But I don't obtain the same result for RestExpr :

RestExpr ::= + Mult Expr
             |- Mult Expr
             | (* nothing *)

Am I wrong ? (and why ?)

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Another question (totally different) :
I've created the type :
type expr = Plus of expr * expr
           | Minus of expr * expr
           | Div of expr * expr
           | Sin of expr
           | Cos of expr
[etc... (not important)]

when I match an expression, I do for instance :
Plus (u, v) -> blablabla (u, v)
Minus (u, v) -> blablabla (u, v) (same result as above)
Div (u, v) -> a different result

Can I reduce the code in order to do such a thing :
Div (u, v) -> blabliblou
BinaryFunction (u, v) -> blablabla (u, v)

(BinaryFunction match for both Plus and Minus (all the others binary 
functions))

Thank you (maybe should I have written in french ?)