Exactly. And I do not see zeroes as fewer variables, but as more constraints. The two points of view are actually equivalent. If you have actual variables for t

Exactly. And I do not see zeroes as fewer variables, but as more constraints. The two points of view are actually equivalent. If you have actual variables for the digits that need to be zero, you can either get rid of these variables and replace them with zero everywhere else or you simply add constraints that require those digits to be zero.