[sv-ec] virtual method modifier - optional?

There is no statement in LRM which defines if virtual keyword is optional
for virtual function. 
Consider below example
 
class B;
    function void f; $display("b");endfunction 
    //this function is overriden by virtual fucntion in child class. is it
allowed? is this function virtual???
endclass
 

class C extends B;
    virtual function void f;$display("c"); endfunction
    //this function is overrides nonvirtual from base class - is it allowed?

endclass
 
class D extends C;
         function void f;$display("d"); endfunction  
        //this function declaration skips virtual keyword : is it legal? is
this function still virtual?
endclass
 
B b=new; C c=new; D d=new;
 
        initial begin
                b.f;
                b=c;
                b.f;
                c.f;
                b=d;c=d;
                b.f;
                c.f;
                d.f;
        end
 
endmodule

 
 
Assuming that above should compile we may get 2 different results:
Result 1:
b
b
c
b
d
d
 
Result 2:
b
c
c
d
d
d
 
IMHO LRM should have explicit rules for above. and result 1 should be
correct.
 
DANiel

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