Focus consists of that part of the sentence that introduces new information not deducible from the context, which is more communicatively important than topic and cannot be omitted from the sentence.
We assume that the focus is necessarily present in each sentence.
We assume that in a tectogrammatical tree, the focus consists of the following nodes:
the effective root of the sentence (the node representing the governing verb) its tfa value is f;
nodes with the value f in the attribute tfa dependent on the effective root and all their descendant nodes;
those more deeply embedded nodes with the value f in the attribute tfa that depend on a node with the value t
In the tectogrammatical trees, the focus is placed on the right.