Quasi-questionnaires, codes and Huffman's length

New concepts are defined, in particular the quasi-question or vertex with an outgoing arc of zero probability. A quasi-questionnaire is a probabilistic homogeneous (rooted) tree with quasiquestions. It is shown that every instantaneous code is a quasi-questionnaire with precise restrictive conditions; it may also be a questionnaire, without an arc of zero probability. Also, an approximation is given — without use of the classical construction —of the average length of Huffman's code with a given alphabet and given probabilities of code-words.