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A double stop is the act of playing two notes simultaneously on a string instrument. In performing a double stop, two separate strings are depressed (stopped with fingers).
A double bar with dots is a repeat sign. It means go back to the beginning and play the whole section again. If the dots are on the left of the lines go either back to the beginning or look for one...
The barline divides music into measures, which are the smallest metrical divisions in a composition. A measure contains a fixed number of beats and is marked off by a vertical line called a "bar",...