Help. Press Alt with the appropriate letter. For example, to type ⊂, ⊆ or ⊄, hold Alt and press C one, two or three times.. Stop the mouse over each button to learn its keyboard shortcut. Shift + click a button to insert its upper-case form. Alt + click a button to copy a single character to the clipboard.. You can select text and press Ctrl + C to copy it to your docu­ment.