  We propose and discuss some toy models of stock markets using the same
operatorial approach adopted in quantum mechanics. Our models are suggested by
the discrete nature of the number of shares and of the cash which are exchanged
in a real market, and by the existence of conserved quantities, like the total
number of shares or some linear combination of cash and shares. The same
framework as the one used in the description of a gas of interacting bosons is
adopted.
