You are given a grid filled with hubs with numbers on them. Your objective is to draw lines between them while following these rules:
The inventor of this puzzle type is unknown.
To draw a line, left-click and drag from one hub to another. You can mark a dot as unused by dragging between hubs with the right mouse button.
You can also use the keyboard. Use the arrow keys to move the cursor on top of a dot, then press Enter to draw a line or Space to mark it.
Because a diagonal line visibly blocks the other diagonal of the same square, drawing one rules its crossing out for you, and erasing the line takes that mark away again. While the line stands, the crossing can’t be toggled by hand.
A hub is grayed out once it carries as many lines as its number asks for. That’s a visual reminder only — the hub stays fully editable — and it can be switched off in the game’s preferences.
These parameters are available from the ‘Custom…’ option on the ‘Type’ menu.