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> Square plus one equals sun
For example, as 十 ( cross ) in the Kan-characters (漢字) means 10 ( ten ), 口 + 10 = 口 + 十 = 田 ( rice field ) holds.
In this case, 2 + 2 in the left side means to surround a cross ( 十 ) with two vertical bars and two horizontal bars namely to form 田 in the Kan-characters.
On the other hand, in fact, 5 in the right side means the number of strokes to draw 田 .
However, it's very hard for people except for Chinese and Japanese that are familiar with Kan-characters to find out such a cryptic message.