Section Header
    + name := G_BINARY_EXPR;
    - comment := "Binary operator";
    - author := "Benoit Sonntag (bsonntag@loria.fr)";
Section Inherit
    + parent_g_expr:Expanded G_EXPR;
Section Public
    + right:G_EXPR;
    + left:G_EXPR;
Creation.
    - create l:G_EXPR and r:G_EXPR :SELF <-
    - make l:G_EXPR and r:G_EXPR <-
Refresh.
    - refresh <-