The flag of Switzerland has the shape of which mathematical symbol on it?

Addition

The national flag of Switzerland displays a white cross in the center of a square red field. The white addition symbol is known as the Swiss cross or the federal cross. Its arms are equilateral and their ratio of length to width is 7:6. The size of the cross in relation to the field was set in 2017 as 5:8. 

The cross has been used as the field sign of the Old Swiss Confederacy since its formation in the last 13th or early 14th century. Its symbolism was described by the Swiss Federal Council in 1889 as representing at the same the Christian cross symbol and the field sign of the Old Confederacy. 

As a national ensign, it was first used during the Napoleonic Wars by General Niklaus Franz von Bachmann, and as the regimental flag of all cantonal troops from 1841. 

The current design was used together with a cross composed of five squares until 1889 when its dimensions were officially set. The civil and state ensign of Switzerland, used by Swiss ships boats, and non-governmental bodies, is rectangular in shape and has the more common proportions of 2:3.  The emblem of the Red Cross is the Swiss flag with switched colors. The Swiss flag is one of only two square sovereign-state flags, the other being the flag of Vatican City. 

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