Logisim - Tunnel that outputs the OR result of all of its inputs
In Logisim, a tunnel is just a hidden wire &mdash; all tunnels with the same name (in this case, "Tunnel"), are effectively connected together.

When you try to force two instances of the same tunnel to different values, anything that tries to evalulate the value (including a third tunnel) will show an error.

To create a new signal that is a logical OR of one or more existing signals, you need to instantiate an actual OR gate.