hierarchical trees

Hi all and thanx in advance...

There is a command in Oracle which is "connect by prior" and i think it's a function to build "hierarchical trees", so where can I find the source of this function, or if anybody knows it please tell me...

What i mean is there would be an SQL function before "connect by prior" function written...

Example... I can write a function called called sub

function sub(x,y)
{
Z= X - Y
return z
}

So and then in my program i can use z=sub(5,3) instead of z=5-3, i think connect by prior is same thing but of course longer coding..... Where can i get this code?

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