Open the file demo5.gpn. Teacher New is absent on Monday. He would have four lessons on this day. The first period shall be cancelled. Place the cursor in the substitution line and click on the button <Delete>
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Another click on this button changes the cancellation again to an open substitution.

Hint: Display only open substitutions
You can display only these substitutions that still need to be edited by ticking the box "Uncovered Substitutions".