  Geometric interpretation of the Hirota equation is presented as equation
describing the Laplace sequence of two-dimensional quadrilateral lattices.
Different forms of the equation are given together with their geometric
interpretation: (i) the discrete coupled Volterra system for the coefficients
of the Laplace equation, (ii) the gauge invariant form of the Hirota equation
for projective invariants of the Laplace sequence, (iii) the discrete Toda
system for the rotation coefficients, (iv) the original form of the Hirota
equation for the tau-function of the quadrilateral lattice.
