  Constructivists (and intuitionists in general) asked what kind of mental
construction is needed to convince ourselves (and others) that some
mathematical statement is true. This question has a much more practical (and
even cynical) counterpart: a student of a mathematics class wants to know what
will the teacher accept as a correct solution of a homework problem. Here the
logical structure of the claim is also very important, and we discuss several
types of problems and their use in teaching mathematics.
