  In the first part of planned series of papers the formal general solutions to
selection of 80 examples of different types of second order nonlinear PDEs in
two independent variables with constant parameters are given. The main goal
here is to show on examples the types of solvable PDEs and what their general
solutions look like. The solving strategy, used here, as a rule is the order
reduction. The order reduction method is implemented in Maple procedure, which
applicable to PDEs of different order with different number of independent
variables. Some of given PDEs are solved by order lifting to PDEs, which are
solvable by the subsequent order reduction.
