If your keymap is configured with an AltGr key, you can also press Ctrl+Alt simulatenously to get the same effect. This can be useful in some cases, for example on many AltGr-style keymaps, the '@' character is on AltGr + 2. This would normally require both hands, unless you want to stretch your left hand all over the keyboard (not good for fast typing), so instead you can do (left)ctrl+alt+2, which is pretty easy to do with one hand.